On 08/09/2023 15:46, Javier Martinez Canillas wrote:
Thomas Zimmermann <tzimmermann@xxxxxxx> writes:
Hello Thomas,
Hi Maxime
Am 08.09.23 um 12:58 schrieb Maxime Ripard:
Hi,
On Fri, Sep 08, 2023 at 11:21:51AM +0200, Thomas Zimmermann wrote:
Am 25.08.23 um 16:04 schrieb Jocelyn Falempe:
[...]
+ *
+ * But there are two exceptions only for dumb buffers:
+ * * To support XRGB8888 if it's not supported by the hardware.
+ * * Any driver is free to modify its internal representation of the format,
+ * as long as it doesn't alter the visible content in any way, and doesn't
+ * modify the user-provided buffer. An example would be to drop the
+ * padding component from a format to save some memory bandwidth.
I have strong objections to this point, _especially_ as you're apparently
trying to sneak this in after our discussion.
I think it's an unfair characterization. This was discussed on
#dri-devel, and went through several rounds over the mailing lists, with
you in Cc for each. How is that sneaking something in?
A few months ago, we had a flamewar'ish IRC discussion on format
conversion within the kernel. The general sentiment was that the kernel
drivers should use what ever is provided by userspace without further
processing. The short argument was 'userspace knows better'. The only
exception is for supporting XRGB8888 on hardware that would otherwise
not support it. After some consideration, I agree with all that. (Back
then I didn't.)
I wasn't part of this "flamewar", and though my patch was a bit
unrelated to this. That's why I started this work to document clearly
what is acceptable in the kernel or not. I discuss it on IRC, and then
proposed the patch on dri-devel to find a compromise, and see if my case
can be acceptable or not.
A few weeks ago I received a patch to do an implicit conversion from
XRGB8888 to RGB888 within mgag200. [1] I don't have a link to the
discussion, but I NAK'ed that patch pretty hard on IRC by following that
other discussion.
And know I find that this patch (even in its v1) contains language that
retroactively legitimizes the mgag200 patch. I wrote 'apparently' I my
reply, as I assume that there's more to it, but how does it not look
like an attempt to sneak in something that is known to be controversial?
That was not my intention, and I apologize if you feel it this way. My
goal was just to clarify if this optimization is acceptable for other
kernel developers, since I though you were willing to accept it, but
some other developers from the "flamewar" were against.
While is true that the motivation for Jocelyn's patch was to make explicit
what are the rules with regard to drivers emulating formats (other than
"we had a flamewar on IRC a while back" which is quite ambiguous), it was
not attempt to sneak something that is known to be controversial.
In fact, it is an attempt to dispel the controversy and document what is
acceptable and what is not for a driver.
It might have been better to discuss the question separately on the
dri-devel ML. Maybe we can do this here.
This was discussed in the #dri-devel IRC channel, I believe you were on
PTO at the time and probably that's why you missed. I found the logs here:
https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2023-08-04
As you can see there, most people agreed that what Jocelyn wrote in his
doc patch is the most pragmatic compromise.
Best regards,
--
Jocelyn
