[PATCH 18/28] drm/amd/display: Remove unnecessary DC_FP_START/DC_FP_END

[Alex Deucher]

On Tue, Apr 29, 2025 at 12:01 PM Alex Hung <alex.hung at amd.com> wrote:
>
>
>
> On 4/29/25 09:04, Alex Deucher wrote:
> > On Mon, Apr 28, 2025 at 9:57 AM Ray Wu <ray.wu at amd.com> wrote:
> >>
> >> From: Alex Hung <alex.hung at amd.com>
> >>
> >> [WHY & HOW]
> >> Remove the unnecessary DC_FP_START/DC_FP_END pair to reduce time in
> >> preempt_disable. It also fixes "BUG: sleeping function called from
> >> invalid context" error messages because of calling kzalloc with
> >> GFP_KERNEL which can sleep.
> >
> > Is this safe?  If this function uses FP or calls a function which uses
> > FP, removing these will lead to register corruption.
>
> I checked dcn32_resource_construct again and I did not find any FP or
> functions uses FP, and Aurabindo helped double check.
>
> I also checked other dnc*_resource_construct (like 321, 35, 351, 36) and
> they don't use DC_FP_START/DC_FP_END pair either.
>
> So it should be safe to remove this pair.

Great.  Thanks for verifying.

Alex

>
> >
> > Alex
> >
> >>
> >> Reviewed-by: Aurabindo Pillai <aurabindo.pillai at amd.com>
> >> Signed-off-by: Alex Hung <alex.hung at amd.com>
> >> Signed-off-by: Ray Wu <ray.wu at amd.com>
> >> ---
> >>   .../gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c  | 6 ------
> >>   1 file changed, 6 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c b/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c
> >> index 2a59cc61ed8c..944650cb13de 100644
> >> --- a/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c
> >> +++ b/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c
> >> @@ -2114,8 +2114,6 @@ static bool dcn32_resource_construct(
> >>   #define REG_STRUCT dccg_regs
> >>          dccg_regs_init();
> >>
> >> -       DC_FP_START();
> >> -
> >>          ctx->dc_bios->regs = &bios_regs;
> >>
> >>          pool->base.res_cap = &res_cap_dcn32;
> >> @@ -2501,14 +2499,10 @@ static bool dcn32_resource_construct(
> >>          if (ASICREV_IS_GC_11_0_3(dc->ctx->asic_id.hw_internal_rev) && (dc->config.sdpif_request_limit_words_per_umc == 0))
> >>                  dc->config.sdpif_request_limit_words_per_umc = 16;
> >>
> >> -       DC_FP_END();
> >> -
> >>          return true;
> >>
> >>   create_fail:
> >>
> >> -       DC_FP_END();
> >> -
> >>          dcn32_resource_destruct(pool);
> >>
> >>          return false;
> >> --
> >> 2.43.0
> >>
>