Hi Tomasz, On Mon, Jun 10, 2019 at 5:48 AM Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote: > > Hi Maxime, > > On Sun, Jun 9, 2019 at 11:38 PM Maxime Jourdan <mjourdan@xxxxxxxxxxxx> wrote: > > > > Add a enum_fmt format flag to specifically tag coded formats where > > dynamic resolution switching is supported by the device. > > > > This is useful for some codec drivers that can't support dynamic > > resolution switching for all their listed coded formats. It allows > > userspace to know whether it should extract the video parameters itself, > > or if it can rely on the device to send V4L2_EVENT_SOURCE_CHANGE when > > such changes are detected. > > > > First of all, thanks for the patch! > > Given the aspect of compatibility and also the general preference for > the drivers to actually handle dynamic resolution changes, I'd suggest > inverting the meaning of this flag. With something like > "V4L2_FMT_FLAG_STATIC_RESOLUTION" it would be more of an exception > rather than the default behavior. > This is actually what I did to begin with [0], with the same reasoning: not supporting dynamic resolution for a certain coded format is more of an exception than the norm (for decoders). The patch was ultimately dropped from the meson vdec series after discussing with Hans, see [0] or the lkml link Hans provided in his answer. We have the chance today that stateful decoders in the kernel either support V4L2_EVENT_SOURCE_CHANGE and dynamic resolution switching for all their formats, or they don't expose V4L2_EVENT_SOURCE_CHANGE at all. While this flag would change the spec, it wouldn't break existing userspace using close-to-spec drivers like s5p-mfc or mtk-vcodec. Cheers, Maxime [0] https://patchwork.kernel.org/patch/10969829/ > Best regards, > Tomasz
