netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 123 insertions, 0 deletions

diff --git a/drivers/mfd/atmel-flexcom.c b/drivers/mfd/atmel-flexcom.c
new file mode 100644
index 000000000..d5df5466e
--- /dev/null
+++ b/drivers/mfd/atmel-flexcom.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Driver for Atmel Flexcom
+ *
+ * Copyright (C) 2015 Atmel Corporation
+ *
+ * Author: Cyrille Pitchen <cyrille.pitchen@atmel.com>
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/clk.h>
+#include <dt-bindings/mfd/atmel-flexcom.h>
+
+/* I/O register offsets */
+#define FLEX_MR		0x0	/* Mode Register */
+#define FLEX_VERSION	0xfc	/* Version Register */
+
+/* Mode Register bit fields */
+#define FLEX_MR_OPMODE_OFFSET	(0)  /* Operating Mode */
+#define FLEX_MR_OPMODE_MASK	(0x3 << FLEX_MR_OPMODE_OFFSET)
+#define FLEX_MR_OPMODE(opmode)	(((opmode) << FLEX_MR_OPMODE_OFFSET) &	\
+				 FLEX_MR_OPMODE_MASK)
+
+struct atmel_flexcom {
+	void __iomem *base;
+	u32 opmode;
+	struct clk *clk;
+};
+
+static int atmel_flexcom_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct atmel_flexcom *ddata;
+	int err;
+
+	ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
+	if (!ddata)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, ddata);
+
+	err = of_property_read_u32(np, "atmel,flexcom-mode", &ddata->opmode);
+	if (err)
+		return err;
+
+	if (ddata->opmode < ATMEL_FLEXCOM_MODE_USART ||
+	    ddata->opmode > ATMEL_FLEXCOM_MODE_TWI)
+		return -EINVAL;
+
+	ddata->base = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
+	if (IS_ERR(ddata->base))
+		return PTR_ERR(ddata->base);
+
+	ddata->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(ddata->clk))
+		return PTR_ERR(ddata->clk);
+
+	err = clk_prepare_enable(ddata->clk);
+	if (err)
+		return err;
+
+	/*
+	 * Set the Operating Mode in the Mode Register: only the selected device
+	 * is clocked. Hence, registers of the other serial devices remain
+	 * inaccessible and are read as zero. Also the external I/O lines of the
+	 * Flexcom are muxed to reach the selected device.
+	 */
+	writel(FLEX_MR_OPMODE(ddata->opmode), ddata->base + FLEX_MR);
+
+	clk_disable_unprepare(ddata->clk);
+
+	return devm_of_platform_populate(&pdev->dev);
+}
+
+static const struct of_device_id atmel_flexcom_of_match[] = {
+	{ .compatible = "atmel,sama5d2-flexcom" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, atmel_flexcom_of_match);
+
+static int __maybe_unused atmel_flexcom_resume_noirq(struct device *dev)
+{
+	struct atmel_flexcom *ddata = dev_get_drvdata(dev);
+	int err;
+	u32 val;
+
+	err = clk_prepare_enable(ddata->clk);
+	if (err)
+		return err;
+
+	val = FLEX_MR_OPMODE(ddata->opmode);
+	writel(val, ddata->base + FLEX_MR);
+
+	clk_disable_unprepare(ddata->clk);
+
+	return 0;
+}
+
+static const struct dev_pm_ops __maybe_unused atmel_flexcom_pm_ops = {
+	.resume_noirq = atmel_flexcom_resume_noirq,
+};
+
+static struct platform_driver atmel_flexcom_driver = {
+	.probe	= atmel_flexcom_probe,
+	.driver	= {
+		.name		= "atmel_flexcom",
+		.pm		= pm_ptr(&atmel_flexcom_pm_ops),
+		.of_match_table	= atmel_flexcom_of_match,
+	},
+};
+
+module_platform_driver(atmel_flexcom_driver);
+
+MODULE_AUTHOR("Cyrille Pitchen <cyrille.pitchen@atmel.com>");
+MODULE_DESCRIPTION("Atmel Flexcom MFD driver");
+MODULE_LICENSE("GPL v2");