Hi Nicolas, Thanks for the review. On 15/05/24 01:52, Nicolas Dufresne wrote: > Le samedi 11 mai 2024 à 22:38 +0530, Devarsh Thakkar a écrit : >> Hi Andy, >> >> Thanks for the quick review. >> On 10/05/24 20:40, Andy Shevchenko wrote: >>> On Fri, May 10, 2024 at 12:10:01AM +0530, Devarsh Thakkar wrote: >>>> If neither of the flags to round down (V4L2_SEL_FLAG_LE) or round up >>>> (V4L2_SEL_FLAG_GE) are specified by the user, then round to nearest >>>> multiple of requested value while updating the crop rectangle coordinates. >>>> >>>> Use the rounding macro which gives preference to rounding down in case two >>>> nearest values (high and low) are possible to raise the probability of >>>> cropping rectangle falling inside the bound region. >>> >>> This is arguable. How do we know that the bigger range is supported? >>> The safest side is to go smaller than bigger. >>> >> >> Yes and that's what the driver does when do when application passes >> while doing the selection. If application does not >> specify explicitly whether to round down or round up the cropping >> parameters requested by it (i.e app is neither passing V4L2_SEL_FLAG_LE >> nor V4L2_SEL_FLAG_GE flags), then it is preferred by driver to round the >> cropping parameters to nearest possible value by either rounding down or >> rounding up to align with hardware requirements. >> >> For e.g. If requested width for cropping region is 127 and HW requires >> width to be multiple of 64 then we would prefer to round it up to 128 >> rather than rounding down to a more distant value (i.e. 64), but if >> requested cropping width is 129 then we would prefer to instead round it >> down to 128. But if requested cropping width is 160 then there are two >> nearest possible values 160 - 32 = 128 and 160 + 32 = 192 and in which >> case we prefer the smaller value as you suggested and that's why the >> driver uses round_closest_down. >> >> For any reason, if still the cropping rectangle falls beyond the bound >> region, then driver will return out of range error (-ERANGE) to >> application. > > I would appreciate if this change was based on specification text, meaning > improving the next if that behaviour is undefined. We might not be able to fix > it everywhere, but we can recommend something. > Yes, this change is based on specification text. This complies with the VIDIOC_G_SELECTION, VIDIOC_S_SELECTION ioctl description as documented in v4l uapi [1] which means driver should choose crop rectangle as close as possible if no flags are passed by user-space, as quoted below : "``0`` - The driver can adjust the rectangle size freely and shall choose a crop/compose rectangle as close as possible to the requested one." If the user-space has specific requirement to either round down, round up or honor exact values, it should pass V4L2_SEL_FLAG_LE, V4L2_SEL_FLAG_GE or V4L2_SEL_FLAG_LE | V4L2_SEL_FLAG_GE flags respectively. [1] https://www.kernel.org/doc/Documentation/userspace-api/media/v4l/vidioc-g-selection.rst#:~:text=compose%20rectangle%20as-,close,-as%20possible%20to Regards Devarsh
