Re: [PATCH v3 02/25] drm/dumb-buffers: Provide helper to set pitch and size

Thomas Zimmermann
2025-02-20T10:05:23Z

Hi

Am 20.02.25 um 10:18 schrieb Tomi Valkeinen:
[...]
>> + * Color modes of 10, 12, 15, 30 and 64 are only supported for use by
>> + * legacy user space. Please don't use them in new code. Other modes
>> + * are not support.
>> + *
>> + * Do not attempt to allocate anything but linear framebuffer memory
>> + * with single-plane RGB data. Allocation of other framebuffer
>> + * layouts requires dedicated ioctls in the respective DRM driver.
>
> According to this, every driver that supports, say, NV12, should
> implement their own custom ioctl to do the exact same thing? And, of
> course, every userspace app that uses, say, NV12, should then add code
> for all these platforms to call the custom ioctls?

Yes, that's exactly the current status.

There has been discussion about a new dumb-create ioctl that takes a DRM
format as parameter. I'm all for it, but it's out of the scope for this
series.

>
> As libdrm's modetest currently supports YUV formats with dumb buffers,
> should we remove that code, as it's not correct and I'm sure people
> use libdrm code as a reference?

Of course not.

>
> Well, I'm not serious above, but I think all my points from the
> earlier version are still valid. I don't like this. It changes the
> parameters of the ioctl (bpp used to be bits-per-pixel, not it's
> "color mode"), and the behavior of the ioctl, behavior that we've had
> for a very long time, and we have no idea how many users there are
> that will break (could be none, of course). And the documentation
> changes make the current behavior and uses wrong or legacy.

Before I go into details about this statement, what use case exactly are
you referring to when you say that behavior changes?

Best regards
Thomas

>
> Clearly we need something new and better for the buffer allocation,
> but for the time being, I'd be more comfortable just keep the current
> behavior, at least for all the drivers I use or maintain: omapdrm,
> tidss, renesas, xlnx, tilcdc.
>
>  Tomi
>

--
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Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
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