Re: [alsa-devel] [PATCH 2/4] acpi: allow for an override to set _REV

On Thursday, May 14, 2015 03:31:26 PM Dominik Brodowski wrote:

By using a module parameter named acpi.supported_rev=<value>, the BIOS may be told a different supported ACPI revision compared to the default (which currently is 5, but will be modified to 2 when the revert of b1ef29725865 is reverted).

Signed-off-by: Dominik Brodowski linux@dominikbrodowski.net

Documentation/kernel-parameters.txt | 14 ++++++++++++++ drivers/acpi/osl.c | 16 ++++++++++++++++ 2 files changed, 30 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 61ab162..75f1f8e 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -335,6 +335,20 @@ bytes respectively. Such letter suffixes can also be entirely omitted. to assume that this machine's pmtimer latches its value and always returns good values.

• acpi.rev= [HW,ACPI]

• 	Tell ACPI BIOS the supported ACPI REV
  

• 	Format: <int> in range 0..5
  

• 	Up to and including Linux v4.1, the BIOS was told which
  

• 	ACPI revision the ACPICA subsystem in Linux actually
  

• 	supports (which was 5 at the time); from v4.2 on, this
  

• 	value will be set statically to 2 to match the behavior
  

• 	of other ACPI implementations. As some BIOS may operate
  

• 	differently depending on which value _REV is set to, this
  

• 	parameter offers the capability to specify what to export
  

• 	to the BIOS. Note that such changes in the behavior of
  

• 	the BIOS may only be visible after cold booting the
  

• 	system with this parameter _twice_.
  

• acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode Format: { level | edge | high | low }

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c index db14a66..caa52f7 100644 --- a/drivers/acpi/osl.c +++ b/drivers/acpi/osl.c @@ -538,6 +538,11 @@ acpi_os_get_physical_address(void *virt, acpi_physical_address * phys)

static char acpi_os_name[ACPI_MAX_OVERRIDE_LEN];

+/* acpi_supported_rev is 0 in case of no override; overrides are limited to

• • values between 1 to 5. To simplify casting, use an unsigned long */

+static unsigned long acpi_supported_rev; +module_param_named(rev, acpi_supported_rev, ulong, 0);

acpi_status acpi_os_predefined_override(const struct acpi_predefined_names *init_val, char **new_val) @@ -552,6 +557,17 @@ acpi_os_predefined_override(const struct acpi_predefined_names *init_val, *new_val = acpi_os_name; }

• if (!memcmp(init_val->name, "_REV", 4) && (acpi_supported_rev > 0)) {

• if (acpi_supported_rev <= 5) {
  

So the only value that would really make sense here is 5.

1 should never ever be used with Linux, 2 is the default, 3 is equivalent to 5 for all practical purposes and 4 has never been used in practice, so it is meaningless.

I'd be better to rename the command line switch to acpi.rev_override and simply do "acpi_supported_rev = 5" for it as well as in acpi_set_supported_rev() in [3/4].

• 	printk(KERN_INFO PREFIX
  

• 		"Overriding _REV definition to %lu\n",
  

• 		acpi_supported_rev);
  

• 	*new_val = (char *) acpi_supported_rev;
  

• } else
  

• 	printk(KERN_INFO PREFIX
  

• 		"_REV override must be between 1 to 5");
  

• }
• return AE_OK;

}

Rafael