drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validationgrafted

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 <adolfotregosa@gmail.com>
Assisted-by: Claude Code:claude-fable-5-1
Signed-off-by: Adrian Betschart <adrian.betschart@cinemaone.ch>
Reviewed-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Adolfo Rodrigues <adolfotregosa@gmail.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7)

1 files changed, 213 insertions, 0 deletions

diff --git a/drivers/clocksource/i8253.c b/drivers/clocksource/i8253.c
new file mode 100644
index 000000000..b603c25f3
--- /dev/null
+++ b/drivers/clocksource/i8253.c
@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * i8253 PIT clocksource
+ */
+#include <linux/clockchips.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/spinlock.h>
+#include <linux/timex.h>
+#include <linux/module.h>
+#include <linux/i8253.h>
+#include <linux/smp.h>
+
+/*
+ * Protects access to I/O ports
+ *
+ * 0040-0043 : timer0, i8253 / i8254
+ * 0061-0061 : NMI Control Register which contains two speaker control bits.
+ */
+DEFINE_RAW_SPINLOCK(i8253_lock);
+EXPORT_SYMBOL(i8253_lock);
+
+#ifdef CONFIG_CLKSRC_I8253
+/*
+ * Since the PIT overflows every tick, its not very useful
+ * to just read by itself. So use jiffies to emulate a free
+ * running counter:
+ */
+static u64 i8253_read(struct clocksource *cs)
+{
+	static int old_count;
+	static u32 old_jifs;
+	unsigned long flags;
+	int count;
+	u32 jifs;
+
+	raw_spin_lock_irqsave(&i8253_lock, flags);
+	/*
+	 * Although our caller may have the read side of jiffies_lock,
+	 * this is now a seqlock, and we are cheating in this routine
+	 * by having side effects on state that we cannot undo if
+	 * there is a collision on the seqlock and our caller has to
+	 * retry.  (Namely, old_jifs and old_count.)  So we must treat
+	 * jiffies as volatile despite the lock.  We read jiffies
+	 * before latching the timer count to guarantee that although
+	 * the jiffies value might be older than the count (that is,
+	 * the counter may underflow between the last point where
+	 * jiffies was incremented and the point where we latch the
+	 * count), it cannot be newer.
+	 */
+	jifs = jiffies;
+	outb_p(0x00, PIT_MODE);	/* latch the count ASAP */
+	count = inb_p(PIT_CH0);	/* read the latched count */
+	count |= inb_p(PIT_CH0) << 8;
+
+	/* VIA686a test code... reset the latch if count > max + 1 */
+	if (count > PIT_LATCH) {
+		outb_p(0x34, PIT_MODE);
+		outb_p(PIT_LATCH & 0xff, PIT_CH0);
+		outb_p(PIT_LATCH >> 8, PIT_CH0);
+		count = PIT_LATCH - 1;
+	}
+
+	/*
+	 * It's possible for count to appear to go the wrong way for a
+	 * couple of reasons:
+	 *
+	 *  1. The timer counter underflows, but we haven't handled the
+	 *     resulting interrupt and incremented jiffies yet.
+	 *  2. Hardware problem with the timer, not giving us continuous time,
+	 *     the counter does small "jumps" upwards on some Pentium systems,
+	 *     (see c't 95/10 page 335 for Neptun bug.)
+	 *
+	 * Previous attempts to handle these cases intelligently were
+	 * buggy, so we just do the simple thing now.
+	 */
+	if (count > old_count && jifs == old_jifs)
+		count = old_count;
+
+	old_count = count;
+	old_jifs = jifs;
+
+	raw_spin_unlock_irqrestore(&i8253_lock, flags);
+
+	count = (PIT_LATCH - 1) - count;
+
+	return (u64)(jifs * PIT_LATCH) + count;
+}
+
+static struct clocksource i8253_cs = {
+	.name		= "pit",
+	.rating		= 110,
+	.read		= i8253_read,
+	.mask		= CLOCKSOURCE_MASK(32),
+};
+
+int __init clocksource_i8253_init(void)
+{
+	return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE);
+}
+#endif
+
+#ifdef CONFIG_CLKEVT_I8253
+void clockevent_i8253_disable(void)
+{
+	guard(raw_spinlock_irqsave)(&i8253_lock);
+
+	/*
+	 * Writing the MODE register should stop the counter, according to
+	 * the datasheet. This appears to work on real hardware (well, on
+	 * modern Intel and AMD boxes; I didn't dig the Pegasos out of the
+	 * shed).
+	 *
+	 * However, some virtual implementations differ, and the MODE change
+	 * doesn't have any effect until either the counter is written (KVM
+	 * in-kernel PIT) or the next interrupt (QEMU). And in those cases,
+	 * it may not stop the *count*, only the interrupts. Although in
+	 * the virt case, that probably doesn't matter, as the value of the
+	 * counter will only be calculated on demand if the guest reads it;
+	 * it's the interrupts which cause steal time.
+	 *
+	 * Hyper-V apparently has a bug where even in mode 0, the IRQ keeps
+	 * firing repeatedly if the counter is running. But it *does* do the
+	 * right thing when the MODE register is written.
+	 *
+	 * So: write the MODE and then load the counter, which ensures that
+	 * the IRQ is stopped on those buggy virt implementations. And then
+	 * write the MODE again, which is the right way to stop it.
+	 */
+	outb_p(0x30, PIT_MODE);
+	outb_p(0, PIT_CH0);
+	outb_p(0, PIT_CH0);
+
+	outb_p(0x30, PIT_MODE);
+}
+
+static int pit_shutdown(struct clock_event_device *evt)
+{
+	if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt))
+		return 0;
+
+	clockevent_i8253_disable();
+	return 0;
+}
+
+static int pit_set_oneshot(struct clock_event_device *evt)
+{
+	raw_spin_lock(&i8253_lock);
+	outb_p(0x38, PIT_MODE);
+	raw_spin_unlock(&i8253_lock);
+	return 0;
+}
+
+static int pit_set_periodic(struct clock_event_device *evt)
+{
+	raw_spin_lock(&i8253_lock);
+
+	/* binary, mode 2, LSB/MSB, ch 0 */
+	outb_p(0x34, PIT_MODE);
+	outb_p(PIT_LATCH & 0xff, PIT_CH0);	/* LSB */
+	outb_p(PIT_LATCH >> 8, PIT_CH0);	/* MSB */
+
+	raw_spin_unlock(&i8253_lock);
+	return 0;
+}
+
+/*
+ * Program the next event in oneshot mode
+ *
+ * Delta is given in PIT ticks
+ */
+static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
+{
+	raw_spin_lock(&i8253_lock);
+	outb_p(delta & 0xff , PIT_CH0);	/* LSB */
+	outb_p(delta >> 8 , PIT_CH0);		/* MSB */
+	raw_spin_unlock(&i8253_lock);
+
+	return 0;
+}
+
+/*
+ * On UP the PIT can serve all of the possible timer functions. On SMP systems
+ * it can be solely used for the global tick.
+ */
+struct clock_event_device i8253_clockevent = {
+	.name			= "pit",
+	.features		= CLOCK_EVT_FEAT_PERIODIC,
+	.set_state_shutdown	= pit_shutdown,
+	.set_state_periodic	= pit_set_periodic,
+	.set_next_event		= pit_next_event,
+};
+
+/*
+ * Initialize the conversion factor and the min/max deltas of the clock event
+ * structure and register the clock event source with the framework.
+ */
+void __init clockevent_i8253_init(bool oneshot)
+{
+	if (oneshot) {
+		i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT;
+		i8253_clockevent.set_state_oneshot = pit_set_oneshot;
+	}
+	/*
+	 * Start pit with the boot cpu mask. x86 might make it global
+	 * when it is used as broadcast device later.
+	 */
+	i8253_clockevent.cpumask = cpumask_of(smp_processor_id());
+
+	clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE,
+					0xF, 0x7FFF);
+}
+#endif