On Tuesday, 26 May 2026 12:52:31 Central European Summer Time Jani Nikula wrote: > On Tue, 26 May 2026, Nicolas Frattaroli <[email protected]> > wrote: > > HDMI 2.1 redefines previously reserved fields in SCDC for various new > > uses. No version check needs to be performed, as an HDMI 2.0 sink's > > reserved SCDC fields are well-defined to be 0, and any zero-ness of > > these fields for an HDMI 2.0 sink is not a surprise for SCDC parsers for > > HDMI 2.1. > > > > Implement reading and outputting these fields over debugfs. > > > > Signed-off-by: Nicolas Frattaroli <[email protected]> > > --- > > drivers/gpu/drm/display/drm_scdc_helper.c | 154 > > ++++++++++++++++++++++++++---- > > include/drm/display/drm_scdc.h | 9 ++ > > include/drm/display/drm_scdc_helper.h | 85 ++++++++++++++--- > > 3 files changed, 218 insertions(+), 30 deletions(-) > > > > diff --git a/drivers/gpu/drm/display/drm_scdc_helper.c > > b/drivers/gpu/drm/display/drm_scdc_helper.c > > index 75a59c6fc7a5..b5a866372b0f 100644 > > --- a/drivers/gpu/drm/display/drm_scdc_helper.c > > +++ b/drivers/gpu/drm/display/drm_scdc_helper.c > > @@ -21,6 +21,7 @@ > > * DEALINGS IN THE SOFTWARE. > > */ > > > > +#include <linux/bitfield.h> > > #include <linux/export.h> > > #include <linux/i2c.h> > > #include <linux/slab.h> > > @@ -63,6 +64,38 @@ struct scdc_debugfs_priv { > > struct drm_scdc_state state; > > }; > > > > +static __pure const char *drm_scdc_frl_rate_str(enum drm_scdc_frl_rate > > rate) > > There are a total of only 71 __pure usages in the kernel. Is this > helpful for a static function where the compiler can figure it out by > itself?
For the compiler, no. For the programmer, maybe. It's basically documentation that foo(x) remains the same for a specific x, so that having 3 calls with the same parameter in some scope is not actually 3 separate function calls, but just retrieving a value without manually saving it into a stack variable. A compiler can infer that in this case, but a programmer that has their LSP show them the function signature on hover will immediately know what's going on without having to look at the implementation. I have a habit of slapping it onto any function that is pure just because, but if you'd rather have me drop it then I can do that. I'm aware that slapping attributes onto function signatures can make them a bit noisy to read. > Here too, bitfield bit order is implementation defined. See my other > reply in the thread. Ugh, I was hoping that with just 1-byte bitfields, this would not be a problem. If that's not the case, then I guess Bug Endian ruins another handy shortcut. :^( Oh well. Thanks for the reviews, will send a new revision with the comments addressed within the week probably. Kind regards, Nicolas Frattaroli
