linux-kernel - Re: [PATCH v2] mmc: sdhci-pci: Try "cd" for card-detect lookup before using NULL

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Date:   Mon, 12 Nov 2018 13:25:49 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Rajat Jain <rajatja@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rajat Jain <rajatxjain@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dmitry Torokhov <dtor@...gle.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2] mmc: sdhci-pci: Try "cd" for card-detect lookup before
 using NULL

On Mon, Nov 12, 2018 at 1:05 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On 29 October 2018 at 23:17, Rajat Jain <rajatja@...gle.com> 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 "<con_id>-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 <rajatja@...gle.com>
>
> 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 <andriy.shevchenko@...ux.intel.com>
Date:   Tue May 23 20:03:19 2017 +0300

   gpio: acpi: Even more tighten up ACPI GPIO lookups

-- 
With Best Regards,
Andy Shevchenko