Patch "i2c: designware: Do not use parameters from ACPI on Dell Inspiron 7348" has been added to the 4.2-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    i2c: designware: Do not use parameters from ACPI on Dell Inspiron 7348

to the 4.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     i2c-designware-do-not-use-parameters-from-acpi-on-dell-inspiron-7348.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 56d4b8a24cef5d66f0d10ac778a520d3c2c68a48 Mon Sep 17 00:00:00 2001
From: Mika Westerberg <mika.westerberg@linux.intel.com>
Date: Thu, 24 Sep 2015 12:06:54 +0300
Subject: i2c: designware: Do not use parameters from ACPI on Dell Inspiron 7348

From: Mika Westerberg <mika.westerberg@linux.intel.com>

commit 56d4b8a24cef5d66f0d10ac778a520d3c2c68a48 upstream.

ACPI SSCN/FMCN methods were originally added because then the platform can
provide the most accurate HCNT/LCNT values to the driver. However, this
seems not to be true for Dell Inspiron 7348 where using these causes the
touchpad to fail in boot:

  i2c_hid i2c-DLL0675:00: failed to retrieve report from device.
  i2c_designware INT3433:00: i2c_dw_handle_tx_abort: lost arbitration
  i2c_hid i2c-DLL0675:00: failed to retrieve report from device.
  i2c_designware INT3433:00: controller timed out

The values received from ACPI are (in fast mode):

  HCNT: 72
  LCNT: 160

this translates to following timings (input clock is 100MHz on Broadwell):

  tHIGH: 720 ns (spec min 600 ns)
  tLOW: 1600 ns (spec min 1300 ns)
  Bus period: 2920 ns (assuming 300 ns tf and tr)
  Bus speed: 342.5 kHz

Both tHIGH and tLOW are within the I2C specification.

The calculated values when ACPI parameters are not used are (in fast mode):

  HCNT: 87
  LCNT: 159

which translates to:

  tHIGH: 870 ns (spec min 600 ns)
  tLOW: 1590 ns (spec min 1300 ns)
  Bus period 3060 ns (assuming 300 ns tf and tr)
  Bus speed 326.8 kHz

These values are also within the I2C specification.

Since both ACPI and calculated values meet the I2C specification timing
requirements it is hard to say why the touchpad does not function properly
with the ACPI values except that the bus speed is higher in this case (but
still well below the max 400kHz).

Solve this by adding DMI quirk to the driver that disables using ACPI
parameters on this particulare machine.

Reported-by: Pavel Roskin <plroskin@gmail.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Pavel Roskin <plroskin@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/i2c/busses/i2c-designware-platdrv.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/drivers/i2c/busses/i2c-designware-platdrv.c
+++ b/drivers/i2c/busses/i2c-designware-platdrv.c
@@ -24,6 +24,7 @@
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/delay.h>
+#include <linux/dmi.h>
 #include <linux/i2c.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
@@ -51,6 +52,22 @@ static u32 i2c_dw_get_clk_rate_khz(struc
 }
 
 #ifdef CONFIG_ACPI
+/*
+ * The HCNT/LCNT information coming from ACPI should be the most accurate
+ * for given platform. However, some systems get it wrong. On such systems
+ * we get better results by calculating those based on the input clock.
+ */
+static const struct dmi_system_id dw_i2c_no_acpi_params[] = {
+	{
+		.ident = "Dell Inspiron 7348",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Inspiron 7348"),
+		},
+	},
+	{ }
+};
+
 static void dw_i2c_acpi_params(struct platform_device *pdev, char method[],
 			       u16 *hcnt, u16 *lcnt, u32 *sda_hold)
 {
@@ -58,6 +75,9 @@ static void dw_i2c_acpi_params(struct pl
 	acpi_handle handle = ACPI_HANDLE(&pdev->dev);
 	union acpi_object *obj;
 
+	if (dmi_check_system(dw_i2c_no_acpi_params))
+		return;
+
 	if (ACPI_FAILURE(acpi_evaluate_object(handle, method, NULL, &buf)))
 		return;
 


Patches currently in stable-queue which might be from mika.westerberg@linux.intel.com are

queue-4.2/i2c-designware-do-not-use-parameters-from-acpi-on-dell-inspiron-7348.patch
queue-4.2/i2c-designware-platdrv-enable-runtimepm-before-registering-to-the-core.patch