Re: [PATCH] drm/i915: Add a parameter to disable SAGV

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 26 Feb 2018, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> On Mon, Feb 26, 2018 at 03:45:51PM -0800, Azhar Shaikh wrote:
>> SAGV handling is currently broken which can result in system hangs.
>> Add a parameter to disable SAGV, till the SAGV handling is fixed.
>
> Not just handling of the limitations we have with SAGV is broken but
> also probably some hidden DBUF config issue that is worst when SAGV
> is enabled.
>
> But also the handling broken is not a good reason for the parameter
> itself. But the good part of this is the ability to debug display
> hard hangs issues with SAGV requirements.
>
> I'm in favor of the paramenter. We just need a different justification
> here.

*cringe* at adding a parameter to workaround issues.

>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104975
>> Signed-off-by: Azhar Shaikh <azhar.shaikh@intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_params.c | 3 +++
>>  drivers/gpu/drm/i915/i915_params.h | 3 ++-
>>  drivers/gpu/drm/i915/intel_pm.c    | 2 +-
>>  3 files changed, 6 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
>> index 08108ce5be21..6aede52240b0 100644
>> --- a/drivers/gpu/drm/i915/i915_params.c
>> +++ b/drivers/gpu/drm/i915/i915_params.c
>> @@ -167,6 +167,9 @@ struct i915_params i915_modparams __read_mostly = {
>>  i915_param_named_unsafe(enable_dp_mst, bool, 0600,
>>  	"Enable multi-stream transport (MST) for new DisplayPort sinks. (default: true)");
>>  
>> +i915_param_named_unsafe(disable_sagv, bool, 0600,
>> +	"Disable SAGV (default: false)");
>> +
>
> I understand that SAGV is default to enable and enabled by BIOS so we
> actually need to disable it.
>
> However the name will cause the same old confusion as disable power well disable....
>
> So I'm in favor of bool i915.enable_sagv defaults to enable
> and use i915.enable_sagv=0 when we need to disable it.

Agreed, if you must use a parameter.

BR,
Jani.



-- 
Jani Nikula, Intel Open Source Technology Center
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