• Rajat Jain's avatar
    mmc: sdhci-pci: Try "cd" for card-detect lookup before using NULL · cdcefe6b
    Rajat Jain authored
    The card detect IRQ does not work with modern BIOS (that want
    to use _DSD to provide the card detect GPIO to the driver).
    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.
    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: default avatarRajat Jain <rajatja@google.com>
    Acked-by: default avatarAdrian Hunter <adrian.hunter@intel.com>
    Fixes: f10e4bf6
     ("gpio: acpi: Even more tighten up ACPI GPIO lookups")
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarUlf Hansson <ulf.hansson@linaro.org>