On Wed, 24 Jan 2024, Gustavo Sousa <gustavo.sousa@xxxxxxxxx> wrote: > Quoting Yury Norov (2024-01-24 12:27:58-03:00) >>On Wed, Jan 24, 2024 at 08:03:53AM -0600, Lucas De Marchi wrote: >>> On Wed, Jan 24, 2024 at 09:58:26AM +0200, Jani Nikula wrote: >>> > On Tue, 23 Jan 2024, Lucas De Marchi <lucas.demarchi@xxxxxxxxx> wrote: >>> > > From: Yury Norov <yury.norov@xxxxxxxxx> >>> > > >>> > > Generalize __GENMASK() to support different types, and implement >>> > > fixed-types versions of GENMASK() based on it. The fixed-type version >>> > > allows more strict checks to the min/max values accepted, which is >>> > > useful for defining registers like implemented by i915 and xe drivers >>> > > with their REG_GENMASK*() macros. >>> > >>> > Mmh, the commit message says the fixed-type version allows more strict >>> > checks, but none are actually added. GENMASK_INPUT_CHECK() remains the >>> > same. >>> > >>> > Compared to the i915 and xe versions, this is more lax now. You could >>> > specify GENMASK_U32(63,32) without complaints. >>> >>> Doing this on top of the this series: >>> >>> -#define XELPDP_PORT_M2P_COMMAND_TYPE_MASK REG_GENMASK(30, 27) >>> +#define XELPDP_PORT_M2P_COMMAND_TYPE_MASK REG_GENMASK(62, 32) >>> >>> and I do get a build failure: >>> >>> ../drivers/gpu/drm/i915/display/intel_cx0_phy.c: In function ‘__intel_cx0_read_once’: >>> ../include/linux/bits.h:41:31: error: left shift count >= width of type [-Werror=shift-count-overflow] >>> 41 | (((t)~0ULL - ((t)(1) << (l)) + 1) & \ >>> | ^~ I stand corrected. >> >>I would better include this in commit message to avoid people's >>confusion. If it comes to v2, can you please do it and mention that >>this trick relies on shift-count-overflow compiler check? > > Wouldn't it be better to have explicit check that l and h are not out of bounds > based on BITS_PER_TYPE() than relying on a compiler flag that could be turned > off (maybe for some questionable reason, but even so)? My preference would be the explicit check, a comment in code, or an explanation in the commit message, in this order. Because honestly, none of this is obvious, and a future refactoring of GENMASK might just inadvertently thwart the whole check. Regardless, my main concern was moot, on the series, Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx> -- Jani Nikula, Intel
