Linux kernel for uConsole
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cdcefe6bd9
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@google.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
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several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
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the problems which may result by upgrading your kernel.