From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rajat Jain Subject: Re: [PATCH v2] mmc: sdhci-pci: Try "cd" for card-detect lookup before using NULL Date: Mon, 12 Nov 2018 17:26:27 -0800 Message-ID: References: <20181029221701.51376-1-rajatja@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Andy Shevchenko Cc: Ulf Hansson , "Hunter, Adrian" , linux-mmc@vger.kernel.org, Linus Walleij , Rajat Jain , Linux Kernel Mailing List , Mika Westerberg , Andy Shevchenko , Dmitry Torokhov , linux-gpio@vger.kernel.org, linux-acpi@vger.kernel.org List-Id: linux-acpi@vger.kernel.org On Mon, Nov 12, 2018 at 3:26 AM Andy Shevchenko wrote: > > On Mon, Nov 12, 2018 at 1:05 PM Ulf Hansson wrote: > > > > On 29 October 2018 at 23:17, Rajat Jain wrote: > > > Problem: > > > > > > The card detect IRQ does not work with modern BIOS (that want > > > to use _DSD to provide the card detect GPIO to the driver). > > > > > > Details: > > > > > > The mmc core provides the mmc_gpiod_request_cd() API to let host drivers > > > request the gpio descriptor for the "card detect" pin. > > > This pin is specified in the ACPI for the SDHC device: > > > > > > * Either as a resource using _CRS. This is a method used by legacy BIOS. > > > (The driver needs to tell which resource index). > > > > > > * Or as a named property ("cd-gpios"/"cd-gpio") in _DSD (which internally > > > points to an entry in _CRS). This way, the driver can lookup using a > > > string. This is what modern BIOS prefer to use. > > > > > > This API finally results in a call to the following code: > > > > > > struct gpio_desc *acpi_find_gpio(..., const char *con_id,...) > > > { > > > ... > > > /* Lookup gpio (using "-gpio") in the _DSD */ > > > ... > > > if (!acpi_can_fallback_to_crs(adev, con_id)) > > > return ERR_PTR(-ENOENT); > > > ... > > > /* Falling back to _CRS is allowed, Lookup gpio in the _CRS */ > > > ... > > > } > > > > > > Note that this means that if the ACPI has _DSD properties, the kernel > > > will never use _CRS for the lookup (Because acpi_can_fallback_to_crs() > > > will always be false for any device hat has _DSD entries). > > > > > > The SDHCI driver is thus currently broken on a modern BIOS, even if > > > BIOS provides both _CRS (for index based lookup) and _DSD entries (for > > > string based lookup). Ironically, none of these will be used for the > > > lookup currently because: > > > > > > * Since the con_id is NULL, acpi_find_gpio() does not find a matching > > > entry in DSDT. (The _DSDT entry has the property name = "cd-gpios") > > > > > > * Because ACPI contains DSDT entries, thus acpi_can_fallback_to_crs() > > > returns false (because device properties have been populated from > > > _DSD), thus the _CRS is never used for the lookup. > > > > > > Fix: > > > > > > Try "cd" for lookup in the _DSD before falling back to using NULL so > > > as to try looking up in the _CRS. > > > > > > I've tested this patch successfully with both Legacy BIOS (that > > > provide only _CRS method) as well as modern BIOS (that provide both > > > _CRS and _DSD). Also the use of "cd" appears to be fairly consistent > > > across other users of this API (other MMC host controller drivers). > > > > > > Link: https://lkml.org/lkml/2018/9/25/1113 > > > Signed-off-by: Rajat Jain > > > > Applied for fixes, thanks! > > > > Should I add a stable tag to this as well? > > If you go with that it might make sense to have Fixes tag against > > commit f10e4bf6632b5be11cea875b66ba959833a69258 > Author: Andy Shevchenko > Date: Tue May 23 20:03:19 2017 +0300 > > gpio: acpi: Even more tighten up ACPI GPIO lookups > I agree. Thanks, Rajat > -- > With Best Regards, > Andy Shevchenko