On Fri, Oct 31, 2025 at 10:40:13AM +0200, Jani Nikula wrote:
> On Fri, 31 Oct 2025, LiangCheng Wang <[email protected]> wrote:
> > Clang reports that pixpaper_panel_hw_init() exceeds the 8 KB stack
> > frame limit:
> >
> > drivers/gpu/drm/tiny/pixpaper.c:579:12: warning:
> > stack frame size (20024) exceeds limit (8192)
> > in 'pixpaper_panel_hw_init'
> >
> > This warning occurs because the compiler aggressively inlines
> > pixpaper_send_cmd() and pixpaper_send_data() into
> > pixpaper_panel_hw_init(), which inflates the estimated stack usage.
> >
> > Mark these two helper functions as 'noinline' to prevent inlining.
> > This significantly reduces the reported stack usage without changing
> > runtime behavior.
> >
> > Reported-by: kernel test robot <[email protected]>
> > Closes:
> > https://lore.kernel.org/oe-kbuild-all/[email protected]/
> > Fixes: c9e70639f591 ("drm: tiny: Add support for Mayqueen Pixpaper e-ink
> > panel")
> > Signed-off-by: LiangCheng Wang <[email protected]>
> > ---
> > When building with Clang and frame size warnings enabled
> > (-Wframe-larger-than=8192), the compiler reports that
> > pixpaper_panel_hw_init() consumes over 20 KB of stack space:
> >
> > drivers/gpu/drm/tiny/pixpaper.c:579:12: warning:
> > stack frame size (20024) exceeds limit (8192)
> > in 'pixpaper_panel_hw_init'
> >
> > This happens because Clang aggressively inlines
> > pixpaper_send_cmd() and pixpaper_send_data() into
> > pixpaper_panel_hw_init(), causing the calculated stack usage
> > to balloon far beyond the warning threshold.
> >
> > The fix is straightforward: mark these two helper functions as
> > 'noinline' to prevent inlining. This reduces the reported stack
> > usage to within normal limits without changing runtime behavior.
>
> I really *really* wish we wouldn't have to go this route at all.
>
> But if we have to, I think noinline_for_stack is the keyword to use.
For what it's worth, the configuration in the report linked above has
CONFIG_KASAN_STACK=y, which is known to be broken with clang and
requires !COMPILE_TEST to even select it (which the robot should be
using to avoid pathological cases such as this). If I disable
CONFIG_KASAN_STACK, there is no warning even with a 1024 byte limit, so
realistically, I think we can just leave this be.
Cheers,
Nathan
> > ---
> > drivers/gpu/drm/tiny/pixpaper.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/tiny/pixpaper.c
> > b/drivers/gpu/drm/tiny/pixpaper.c
> > index
> > 32598fb2fee7fcdea3ea0696c2bf54404fcffa2e..70e3239adfd0f86f92551991872486380489fb9b
> > 100644
> > --- a/drivers/gpu/drm/tiny/pixpaper.c
> > +++ b/drivers/gpu/drm/tiny/pixpaper.c
> > @@ -536,7 +536,7 @@ static void pixpaper_spi_sync(struct spi_device *spi,
> > struct spi_message *msg,
> > err->errno_code = ret;
> > }
> >
> > -static void pixpaper_send_cmd(struct pixpaper_panel *panel, u8 cmd,
> > +static noinline void pixpaper_send_cmd(struct pixpaper_panel *panel, u8
> > cmd,
> > struct pixpaper_error_ctx *err)
> > {
> > if (err->errno_code)
> > @@ -556,7 +556,7 @@ static void pixpaper_send_cmd(struct pixpaper_panel
> > *panel, u8 cmd,
> > pixpaper_spi_sync(panel->spi, &msg, err);
> > }
> >
> > -static void pixpaper_send_data(struct pixpaper_panel *panel, u8 data,
> > +static noinline void pixpaper_send_data(struct pixpaper_panel *panel, u8
> > data,
> > struct pixpaper_error_ctx *err)
> > {
> > if (err->errno_code)
> >
> > ---
> > base-commit: d127176862a93c4b3216bda533d2bee170af5e71
> > change-id: 20251031-fix_202510270858-2e4643b00545
> >
> > Best regards,
>
> --
> Jani Nikula, Intel
