Maíra Canal <[email protected]> writes: Hello Maíra,
> Hi, > > On 30/09/26 05:32, Thomas Zimmermann wrote: >> Hi >> >> Am 30.09.26 um 09:48 schrieb Javier Martinez Canillas: >> [...] >>>>> I have a patch implementing begin/end_cpu_access to >>>>> drm_gem_prime_dmabuf_ops, which fixed the issue. However, I'm not sure >>>>> we would like to support this use case upstream because, as you >>>>> mentioned, dumb buffers are usually used for software-rendering only. >>>> Before we fix anything, I think we should talk to someone with >>>> dma-buf/PRIME credentials. As I outlined, the ideomatic pattern is a >>>> producer-consumer relationship and HW rendering into dumb-buffers is not >>>> supported. Those buffers should have been allocated on the v3d side. >>>> >>>> IMHO we should write down these rules in the PRIME documentation and >>>> (soft-)enforce them in the implementation. >>>> >>> Yeah, I think either drm_gem_fb_begin_cpu_access() needs to also sync >>> exported buffers (what Maíra is proposing as a fix) or there should be >>> documentation of the rules for cross-devices buffer sharing through >>> PRIME. >> >> This specific case only happens with v3d and only this driver can know >> when to flush caches. If we flush caches in begin_cpu_access, we easily >> end up paying the overhead on all systems. >> > > I believe that's the main issue. We would pay a reasonably big price to > support this uncommon (and maybe even wrong) use case. > > P.S.: To be clear, I wasn't proposing a fix. I should have called my > patch a "hack", because although it works, I don't believe we should > support this use case for the reasons stated by Thomas. > Yes, I agree with you. Making v3d to warn as Thomas suggested seems to be the best compromise. > Best regards, > - Maíra > -- Best regards, Javier Martinez Canillas Core Platforms Red Hat
