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

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Message-ID: <CAPDyKFpqzpxUzZe-ekfwg1Nqeg1RFB1bdbSNwrGPwtfNds4p0w@mail.gmail.com>
Date:   Mon, 12 Nov 2018 12:05:01 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <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>, linux-gpio@...r.kernel.org,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v2] mmc: sdhci-pci: Try "cd" for card-detect lookup before
 using NULL

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?

Kind regards
Uffe

> ---
> v2: Fix the commit log to take care of Andy's comments.
>
>  drivers/mmc/host/sdhci-pci-core.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c
> index 7bfd366d970d..e53333c695b3 100644
> --- a/drivers/mmc/host/sdhci-pci-core.c
> +++ b/drivers/mmc/host/sdhci-pci-core.c
> @@ -1762,8 +1762,13 @@ static struct sdhci_pci_slot *sdhci_pci_probe_slot(
>                 device_init_wakeup(&pdev->dev, true);
>
>         if (slot->cd_idx >= 0) {
> -               ret = mmc_gpiod_request_cd(host->mmc, NULL, slot->cd_idx,
> +               ret = mmc_gpiod_request_cd(host->mmc, "cd", slot->cd_idx,
>                                            slot->cd_override_level, 0, NULL);
> +               if (ret && ret != -EPROBE_DEFER)
> +                       ret = mmc_gpiod_request_cd(host->mmc, NULL,
> +                                                  slot->cd_idx,
> +                                                  slot->cd_override_level,
> +                                                  0, NULL);
>                 if (ret == -EPROBE_DEFER)
>                         goto remove;
>
> --
> 2.19.1.568.g152ad8e336-goog
>