Re: [PATCH] nouveau, ACPI: fix regression caused by b072e53

["Rafael J. Wysocki" <rafael.j.wysocki@intel.com>]

On 2/20/2014 10:23 AM, Jiang Liu wrote:
> Fix regression caused by commit b072e53, which breaks loading nouveau
> driver on optimus laptops.
>
> On some platforms, ACPI _DSM method (nouveau_op_dsm_muid, function 0)
> has special requirements on the fourth parameter, which is different
> from ACPI specifications. So revert to the private implementation
> to check availability of _DSM functions instead of using common
> acpi_check_dsm() interface.
>
> Reported-and-Tested-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
> Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>

I'm taking this, because the commit that introduced the regression went 
in through my tree.

In the future I'll appreciate CCing ACPI-related patches to linux-acpi, 
however.

Thanks,
Rafael


> ---
>   drivers/gpu/drm/nouveau/nouveau_acpi.c |   26 ++++++++++++++++++++++++--
>   1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> index 4ef83df..83face3 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> @@ -106,6 +106,29 @@ static int nouveau_optimus_dsm(acpi_handle handle, int func, int arg, uint32_t *
>   	return 0;
>   }
>   
> +/*
> + * On some platforms, _DSM(nouveau_op_dsm_muid, func0) has special
> + * requirements on the fourth parameter, so a private implementation
> + * instead of using acpi_check_dsm().
> + */
> +static int nouveau_check_optimus_dsm(acpi_handle handle)
> +{
> +	int result;
> +
> +	/*
> +	 * Function 0 returns a Buffer containing available functions.
> +	 * The args parameter is ignored for function 0, so just put 0 in it
> +	 */
> +	if (nouveau_optimus_dsm(handle, 0, 0, &result))
> +		return 0;
> +
> +	/*
> +	 * ACPI Spec v4 9.14.1: if bit 0 is zero, no function is supported.
> +	 * If the n-th bit is enabled, function n is supported
> +	 */
> +	return result & 1 && result & (1 << NOUVEAU_DSM_OPTIMUS_CAPS);
> +}
> +
>   static int nouveau_dsm(acpi_handle handle, int func, int arg)
>   {
>   	int ret = 0;
> @@ -207,8 +230,7 @@ static int nouveau_dsm_pci_probe(struct pci_dev *pdev)
>   			   1 << NOUVEAU_DSM_POWER))
>   		retval |= NOUVEAU_DSM_HAS_MUX;
>   
> -	if (acpi_check_dsm(dhandle, nouveau_op_dsm_muid, 0x00000100,
> -			   1 << NOUVEAU_DSM_OPTIMUS_CAPS))
> +	if (nouveau_check_optimus_dsm(dhandle))
>   		retval |= NOUVEAU_DSM_HAS_OPT;
>   
>   	if (retval & NOUVEAU_DSM_HAS_OPT) {