[PATCH] drm/amd/display: Reduce Stack Usage in 'dp_retrain_link_dp_test' by heap-allocating 'audio_output'

[SHANMUGAM, SRINIVASAN]

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Hung, Alex <Alex.Hung at amd.com>
> Sent: Thursday, July 24, 2025 7:18 AM
> To: SHANMUGAM, SRINIVASAN <SRINIVASAN.SHANMUGAM at amd.com>;
> Pillai, Aurabindo <Aurabindo.Pillai at amd.com>
> Cc: amd-gfx at lists.freedesktop.org; Lin, Wayne <Wayne.Lin at amd.com>; Shen,
> George <George.Shen at amd.com>; Strauss, Michael
> <Michael.Strauss at amd.com>; Mike Katsnelson <mike.katsnelson at amd.com>;
> Lee, Alvin <Alvin.Lee2 at amd.com>; Wu, Ray <Ray.Wu at amd.com>; Liu, Wenjing
> <Wenjing.Liu at amd.com>; Wentland, Harry <Harry.Wentland at amd.com>; Chung,
> ChiaHsuan (Tom) <ChiaHsuan.Chung at amd.com>; Li, Roman
> <Roman.Li at amd.com>
> Subject: Re: [PATCH] drm/amd/display: Reduce Stack Usage in
> 'dp_retrain_link_dp_test' by heap-allocating 'audio_output'
>
>
>
> On 7/21/25 07:06, Srinivasan Shanmugam wrote:
> > The function dp_retrain_link_dp_test currently allocates a large
> > audio_output array on the stack, causing the stack frame size to
> > exceed the compiler limit (1080 bytes > 1024 bytes).
> >
> > This change prevents stack overflow issues:
> > amdgpu/../display/dc/link/accessories/link_dp_cts.c:65:13: warning:
> > stack frame size (1080) exceeds limit (1024) in
> > 'dp_retrain_link_dp_test' [-Wframe-larger-than] static void
> > dp_retrain_link_dp_test(struct dc_link *link,
> >
> > This commit refactors the function to dynamically allocate the
> > audio_output array using kmalloc/kfree, significantly reducing stack
> > usage.
> >
> > - Allocates audio_output on the heap instead of stack
> > - Adds error handling for allocation failure
> > - Frees allocated memory before function return
> >
> > Fixes: 9437059b4bfb ("drm/amd/display: Fix Link Override Sequencing
> > When Switching Between DIO/HPO") Switching Between DIO/HPO")
> > Cc: Wayne Lin <wayne.lin at amd.com>
> > Cc: George Shen <george.shen at amd.com>
> > Cc: Michael Strauss <michael.strauss at amd.com>
> > Cc: Mike Katsnelson <mike.katsnelson at amd.com>
> > Cc: Alvin Lee <Alvin.Lee2 at amd.com>
> > Cc: Ray Wu <ray.wu at amd.com>
> > Cc: Wenjing Liu <wenjing.liu at amd.com>
> > Cc: Harry Wentland <harry.wentland at amd.com>
> > Cc: Tom Chung <chiahsuan.chung at amd.com>
> > Cc: Roman Li <roman.li at amd.com>
> > Cc: Alex Hung <alex.hung at amd.com>
> > Cc: Aurabindo Pillai <aurabindo.pillai at amd.com>
> > Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
> > ---
> >   .../amd/display/dc/link/accessories/link_dp_cts.c   | 13 ++++++++++++-
> >   1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git
> > a/drivers/gpu/drm/amd/display/dc/link/accessories/link_dp_cts.c
> > b/drivers/gpu/drm/amd/display/dc/link/accessories/link_dp_cts.c
> > index 2956c2b3ad1a..c4db61cb5079 100644
> > --- a/drivers/gpu/drm/amd/display/dc/link/accessories/link_dp_cts.c
> > +++ b/drivers/gpu/drm/amd/display/dc/link/accessories/link_dp_cts.c
> > @@ -75,7 +75,16 @@ static void dp_retrain_link_dp_test(struct dc_link *link,
> >     bool is_hpo_acquired;
> >     uint8_t count;
> >     int i;
> > -   struct audio_output audio_output[MAX_PIPES];
> > +
> > +   /* Dynamically allocate audio_output to reduce stack usage */
> > +   struct audio_output *audio_output;
> > +
> > +   audio_output = kmalloc(sizeof(*audio_output) * MAX_PIPES,
> > +GFP_KERNEL);
>
> This file is shared with another OS which has no kmalloc call, and unfortunately this
> change does not pass CI.
>

Thanks Alex!, will propose v2 for this.

Srini

>
> > +   if (!audio_output) {
> > +           /* Allocation failed, handle error gracefully */
> > +           DC_LOG_ERROR("%s: Failed to allocate audio_output", __func__);
> > +           return;
> > +   }
> >
> >     needs_divider_update = (link->dc->link_srv-
> >dp_get_encoding_format(link_setting) !=
> >     link->dc->link_srv->dp_get_encoding_format((const struct dc_link_settings
> *) &link->cur_link_settings));
> > @@ -144,6 +153,8 @@ static void dp_retrain_link_dp_test(struct dc_link *link,
> >                     stream_update.dpms_off = &dpms_off;
> >                     dc_update_planes_and_stream(state->clk_mgr->ctx->dc,
> NULL, 0, state->streams[i], &stream_update);
> >             }
> > +
> > +   kfree(audio_output);
> >   }
> >
> >   static void dp_test_send_link_training(struct dc_link *link)