From 106b4a2a78b2a2f14885604891957b84bba502db Mon Sep 17 00:00:00 2001 From: Adrian Betschart Date: Fri, 11 Sep 2026 17:13:14 +0200 Subject: drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validation amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and uses the first encoding that validates. YCbCr 4:4:4 is listed before RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the "color format" property is left at AUTO, even though RGB fits the same link. That contradicts the documented AUTO behaviour for HDMI in enum drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when the bandwidth is not available or the mode is 4:2:0-only), which the amdgpu implementation of the property also describes. It also leaves the "Broadcast RGB" property without effect on such sinks, since the quantization range it selects only applies to RGB output. Try RGB first. The mask still holds every encoding the sink supports, so a mode that cannot carry RGB falls back exactly as before. For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI sink that advertised it. Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation") Suggested-by: Adolfo Rodrigues Assisted-by: Claude Code:claude-fable-5-1 Signed-off-by: Adrian Betschart Reviewed-by: Fangzhi Zuo Tested-by: Adolfo Rodrigues Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher (cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7) --- Documentation/cpu-freq/core.rst | 113 ++++++++++++ Documentation/cpu-freq/cpu-drivers.rst | 290 +++++++++++++++++++++++++++++++ Documentation/cpu-freq/cpufreq-stats.rst | 136 +++++++++++++++ Documentation/cpu-freq/index.rst | 36 ++++ 4 files changed, 575 insertions(+) create mode 100644 Documentation/cpu-freq/core.rst create mode 100644 Documentation/cpu-freq/cpu-drivers.rst create mode 100644 Documentation/cpu-freq/cpufreq-stats.rst create mode 100644 Documentation/cpu-freq/index.rst (limited to 'Documentation/cpu-freq') diff --git a/Documentation/cpu-freq/core.rst b/Documentation/cpu-freq/core.rst new file mode 100644 index 000000000..4ceef8e72 --- /dev/null +++ b/Documentation/cpu-freq/core.rst @@ -0,0 +1,113 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================================= +General description of the CPUFreq core and CPUFreq notifiers +============================================================= + +Authors: + - Dominik Brodowski + - David Kimdon + - Rafael J. Wysocki + - Viresh Kumar + +.. Contents: + + 1. CPUFreq core and interfaces + 2. CPUFreq notifiers + 3. CPUFreq Table Generation with Operating Performance Point (OPP) + +1. General Information +====================== + +The CPUFreq core code is located in drivers/cpufreq/cpufreq.c. This +cpufreq code offers a standardized interface for the CPUFreq +architecture drivers (those pieces of code that do actual +frequency transitions), as well as to "notifiers". These are device +drivers or other part of the kernel that need to be informed of +policy changes (ex. thermal modules like ACPI) or of all +frequency changes (ex. timing code) or even need to force certain +speed limits (like LCD drivers on ARM architecture). Additionally, the +kernel "constant" loops_per_jiffy is updated on frequency changes +here. + +Reference counting of the cpufreq policies is done by cpufreq_cpu_get +and cpufreq_cpu_put, which make sure that the cpufreq driver is +correctly registered with the core, and will not be unloaded until +cpufreq_put_cpu is called. That also ensures that the respective cpufreq +policy doesn't get freed while being used. + +2. CPUFreq notifiers +==================== + +CPUFreq notifiers conform to the standard kernel notifier interface. +See linux/include/linux/notifier.h for details on notifiers. + +There are two different CPUFreq notifiers - policy notifiers and +transition notifiers. + + +2.1 CPUFreq policy notifiers +---------------------------- + +These are notified when a new policy is created or removed. + +The phase is specified in the second argument to the notifier. The phase is +CPUFREQ_CREATE_POLICY when the policy is first created and it is +CPUFREQ_REMOVE_POLICY when the policy is removed. + +The third argument, a ``void *pointer``, points to a struct cpufreq_policy +consisting of several values, including min, max (the lower and upper +frequencies (in kHz) of the new policy). + + +2.2 CPUFreq transition notifiers +-------------------------------- + +These are notified twice for each online CPU in the policy, when the +CPUfreq driver switches the CPU core frequency and this change has no +any external implications. + +The second argument specifies the phase - CPUFREQ_PRECHANGE or +CPUFREQ_POSTCHANGE. + +The third argument is a struct cpufreq_freqs with the following +values: + +====== ====================================== +policy a pointer to the struct cpufreq_policy +old old frequency +new new frequency +flags flags of the cpufreq driver +====== ====================================== + +3. CPUFreq Table Generation with Operating Performance Point (OPP) +================================================================== +For details about OPP, see Documentation/power/opp.rst + +dev_pm_opp_init_cpufreq_table - + This function provides a ready to use conversion routine to translate + the OPP layer's internal information about the available frequencies + into a format readily providable to cpufreq. + + .. Warning:: + + Do not use this function in interrupt context. + + Example:: + + soc_pm_init() + { + /* Do things */ + r = dev_pm_opp_init_cpufreq_table(dev, &freq_table); + if (!r) + policy->freq_table = freq_table; + /* Do other things */ + } + + .. note:: + + This function is available only if CONFIG_CPU_FREQ is enabled in + addition to CONFIG_PM_OPP. + +dev_pm_opp_free_cpufreq_table + Free up the table allocated by dev_pm_opp_init_cpufreq_table diff --git a/Documentation/cpu-freq/cpu-drivers.rst b/Documentation/cpu-freq/cpu-drivers.rst new file mode 100644 index 000000000..17c69f836 --- /dev/null +++ b/Documentation/cpu-freq/cpu-drivers.rst @@ -0,0 +1,290 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============================================== +How to Implement a new CPUFreq Processor Driver +=============================================== + +Authors: + + + - Dominik Brodowski + - Rafael J. Wysocki + - Viresh Kumar + +.. Contents + + 1. What To Do? + 1.1 Initialization + 1.2 Per-CPU Initialization + 1.3 verify + 1.4 target/target_index or setpolicy? + 1.5 target/target_index + 1.6 setpolicy + 1.7 get_intermediate and target_intermediate + 2. Frequency Table Helpers + + + +1. What To Do? +============== + +So, you just got a brand-new CPU / chipset with datasheets and want to +add cpufreq support for this CPU / chipset? Great. Here are some hints +on what is necessary: + + +1.1 Initialization +------------------ + +First of all, in an __initcall level 7 (module_init()) or later +function check whether this kernel runs on the right CPU and the right +chipset. If so, register a struct cpufreq_driver with the CPUfreq core +using cpufreq_register_driver() + +What shall this struct cpufreq_driver contain? + + .name - The name of this driver. + + .init - A pointer to the per-policy initialization function. + + .verify - A pointer to a "verification" function. + + .setpolicy _or_ .fast_switch _or_ .target _or_ .target_index - See + below on the differences. + +And optionally + + .flags - Hints for the cpufreq core. + + .driver_data - cpufreq driver specific data. + + .get_intermediate and target_intermediate - Used to switch to stable + frequency while changing CPU frequency. + + .get - Returns current frequency of the CPU. + + .bios_limit - Returns HW/BIOS max frequency limitations for the CPU. + + .exit - A pointer to a per-policy cleanup function called during + CPU_POST_DEAD phase of cpu hotplug process. + + .suspend - A pointer to a per-policy suspend function which is called + with interrupts disabled and _after_ the governor is stopped for the + policy. + + .resume - A pointer to a per-policy resume function which is called + with interrupts disabled and _before_ the governor is started again. + + .ready - A pointer to a per-policy ready function which is called after + the policy is fully initialized. + + .attr - A pointer to a NULL-terminated list of "struct freq_attr" which + allow to export values to sysfs. + + .boost_enabled - If set, boost frequencies are enabled. + + .set_boost - A pointer to a per-policy function to enable/disable boost + frequencies. + + +1.2 Per-CPU Initialization +-------------------------- + +Whenever a new CPU is registered with the device model, or after the +cpufreq driver registers itself, the per-policy initialization function +cpufreq_driver.init is called if no cpufreq policy existed for the CPU. +Note that the .init() and .exit() routines are called only once for the +policy and not for each CPU managed by the policy. It takes a ``struct +cpufreq_policy *policy`` as argument. What to do now? + +If necessary, activate the CPUfreq support on your CPU. + +Then, the driver must fill in the following values: + ++-----------------------------------+--------------------------------------+ +|policy->cpuinfo.min_freq _and_ | | +|policy->cpuinfo.max_freq | the minimum and maximum frequency | +| | (in kHz) which is supported by | +| | this CPU | ++-----------------------------------+--------------------------------------+ +|policy->cpuinfo.transition_latency | the time it takes on this CPU to | +| | switch between two frequencies in | +| | nanoseconds | ++-----------------------------------+--------------------------------------+ +|policy->cur | The current operating frequency of | +| | this CPU (if appropriate) | ++-----------------------------------+--------------------------------------+ +|policy->min, | The min/max scaling frequency. | +|policy->max | If set by the driver in ->init(), | +| | used as the lower/upper bound for | +| | policy frequency QoS requests; | +| | otherwise, reflects the min/max | +| | frequency the driver can set | ++-----------------------------------+--------------------------------------+ +|policy->policy and, if necessary, | | +|policy->governor | must contain the "default policy" for| +| | this CPU. A few moments later, | +| | cpufreq_driver.verify and either | +| | cpufreq_driver.setpolicy or | +| | cpufreq_driver.target/target_index is| +| | called with these values. | ++-----------------------------------+--------------------------------------+ +|policy->cpus | Update this with the masks of the | +| | (online + offline) CPUs that do DVFS | +| | along with this CPU (i.e. that share| +| | clock/voltage rails with it). | ++-----------------------------------+--------------------------------------+ + +For setting some of these values (cpuinfo.min[max]_freq, policy->min[max]), the +frequency table helpers might be helpful. See the section 2 for more information +on them. + + +1.3 verify +---------- + +When the user decides a new policy (consisting of +"policy,governor,min,max") shall be set, this policy must be validated +so that incompatible values can be corrected. For verifying these +values cpufreq_verify_within_limits(``struct cpufreq_policy *policy``, +``unsigned int min_freq``, ``unsigned int max_freq``) function might be helpful. +See section 2 for details on frequency table helpers. + +You need to make sure that at least one valid frequency (or operating +range) is within policy->min and policy->max. If necessary, increase +policy->max first, and only if this is no solution, decrease policy->min. + + +1.4 target or target_index or setpolicy or fast_switch? +------------------------------------------------------- + +Most cpufreq drivers or even most cpu frequency scaling algorithms +only allow the CPU frequency to be set to predefined fixed values. For +these, you use the ->target(), ->target_index() or ->fast_switch() +callbacks. + +Some cpufreq capable processors switch the frequency between certain +limits on their own. These shall use the ->setpolicy() callback. + + +1.5. target/target_index +------------------------ + +The target_index call has two arguments: ``struct cpufreq_policy *policy``, +and ``unsigned int`` index (into the exposed frequency table). + +The CPUfreq driver must set the new frequency when called here. The +actual frequency must be determined by freq_table[index].frequency. + +It should always restore to earlier frequency (i.e. policy->restore_freq) in +case of errors, even if we switched to intermediate frequency earlier. + +Deprecated +---------- +The target call has three arguments: ``struct cpufreq_policy *policy``, +unsigned int target_frequency, unsigned int relation. + +The CPUfreq driver must set the new frequency when called here. The +actual frequency must be determined using the following rules: + +- keep close to "target_freq" +- policy->min <= new_freq <= policy->max (THIS MUST BE VALID!!!) +- if relation==CPUFREQ_REL_L, try to select a new_freq higher than or equal + target_freq. ("L for lowest, but no lower than") +- if relation==CPUFREQ_REL_H, try to select a new_freq lower than or equal + target_freq. ("H for highest, but no higher than") + +Here again the frequency table helper might assist you - see section 2 +for details. + +1.6. fast_switch +---------------- + +This function is used for frequency switching from scheduler's context. +Not all drivers are expected to implement it, as sleeping from within +this callback isn't allowed. This callback must be highly optimized to +do switching as fast as possible. + +This function has two arguments: ``struct cpufreq_policy *policy`` and +``unsigned int target_frequency``. + + +1.7 setpolicy +------------- + +The setpolicy call only takes a ``struct cpufreq_policy *policy`` as +argument. You need to set the lower limit of the in-processor or +in-chipset dynamic frequency switching to policy->min, the upper limit +to policy->max, and -if supported- select a performance-oriented +setting when policy->policy is CPUFREQ_POLICY_PERFORMANCE, and a +powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check +the reference implementation in drivers/cpufreq/longrun.c + +1.8 get_intermediate and target_intermediate +-------------------------------------------- + +Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION unset. + +get_intermediate should return a stable intermediate frequency platform wants to +switch to, and target_intermediate() should set CPU to that frequency, before +jumping to the frequency corresponding to 'index'. Core will take care of +sending notifications and driver doesn't have to handle them in +target_intermediate() or target_index(). + +Drivers can return '0' from get_intermediate() in case they don't wish to switch +to intermediate frequency for some target frequency. In that case core will +directly call ->target_index(). + +NOTE: ->target_index() should restore to policy->restore_freq in case of +failures as core would send notifications for that. + + +2. Frequency Table Helpers +========================== + +As most cpufreq processors only allow for being set to a few specific +frequencies, a "frequency table" with some functions might assist in +some work of the processor driver. Such a "frequency table" consists of +an array of struct cpufreq_frequency_table entries, with driver specific +values in "driver_data", the corresponding frequency in "frequency" and +flags set. At the end of the table, you need to add a +cpufreq_frequency_table entry with frequency set to CPUFREQ_TABLE_END. +And if you want to skip one entry in the table, set the frequency to +CPUFREQ_ENTRY_INVALID. The entries don't need to be in sorted in any +particular order, but if they are cpufreq core will do DVFS a bit +quickly for them as search for best match is faster. + +The cpufreq table is verified automatically by the core if the policy contains a +valid pointer in its policy->freq_table field. + +cpufreq_frequency_table_verify() assures that at least one valid +frequency is within policy->min and policy->max, and all other criteria +are met. This is helpful for the ->verify call. + +cpufreq_frequency_table_target() is the corresponding frequency table +helper for the ->target stage. Just pass the values to this function, +and this function returns the of the frequency table entry which +contains the frequency the CPU shall be set to. + +The following macros can be used as iterators over cpufreq_frequency_table: + +cpufreq_for_each_entry(pos, table) - iterates over all entries of frequency +table. + +cpufreq_for_each_valid_entry(pos, table) - iterates over all entries, +excluding CPUFREQ_ENTRY_INVALID frequencies. +Use arguments "pos" - a ``cpufreq_frequency_table *`` as a loop cursor and +"table" - the ``cpufreq_frequency_table *`` you want to iterate over. + +For example:: + + struct cpufreq_frequency_table *pos, *driver_freq_table; + + cpufreq_for_each_entry(pos, driver_freq_table) { + /* Do something with pos */ + pos->frequency = ... + } + +If you need to work with the position of pos within driver_freq_table, +do not subtract the pointers, as it is quite costly. Instead, use the +macros cpufreq_for_each_entry_idx() and cpufreq_for_each_valid_entry_idx(). diff --git a/Documentation/cpu-freq/cpufreq-stats.rst b/Documentation/cpu-freq/cpufreq-stats.rst new file mode 100644 index 000000000..9ad695b1c --- /dev/null +++ b/Documentation/cpu-freq/cpufreq-stats.rst @@ -0,0 +1,136 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================================== +General Description of sysfs CPUFreq Stats +========================================== + +information for users + + +Author: Venkatesh Pallipadi + +.. Contents + + 1. Introduction + 2. Statistics Provided (with example) + 3. Configuring cpufreq-stats + + +1. Introduction +=============== + +cpufreq-stats is a driver that provides CPU frequency statistics for each CPU. +These statistics are provided in /sysfs as a bunch of read_only interfaces. This +interface (when configured) will appear in a separate directory under cpufreq +in /sysfs (/devices/system/cpu/cpuX/cpufreq/stats/) for each CPU. +Various statistics will form read_only files under this directory. + +This driver is designed to be independent of any particular cpufreq_driver +that may be running on your CPU. So, it will work with any cpufreq_driver. + + +2. Statistics Provided (with example) +===================================== + +cpufreq stats provides following statistics (explained in detail below). + +- time_in_state +- total_trans +- trans_table + +All the statistics will be from the time the stats driver has been inserted +(or the time the stats were reset) to the time when a read of a particular +statistic is done. Obviously, stats driver will not have any information +about the frequency transitions before the stats driver insertion. + +:: + + :/sys/devices/system/cpu/cpu0/cpufreq/stats # ls -l + total 0 + drwxr-xr-x 2 root root 0 May 14 16:06 . + drwxr-xr-x 3 root root 0 May 14 15:58 .. + --w------- 1 root root 4096 May 14 16:06 reset + -r--r--r-- 1 root root 4096 May 14 16:06 time_in_state + -r--r--r-- 1 root root 4096 May 14 16:06 total_trans + -r--r--r-- 1 root root 4096 May 14 16:06 trans_table + +- **reset** + +Write-only attribute that can be used to reset the stat counters. This can be +useful for evaluating system behaviour under different governors without the +need for a reboot. + +- **time_in_state** + +This gives the amount of time spent in each of the frequencies supported by +this CPU. The cat output will have "