Hi Andre,
I'm not familiar with the sample c message optimization. Probably Ken can comment.
However I could check the internal spec here and I saw this bit only exists with this meaning in Haswell.
For all the other platforms, including Broadwell it got re-purposed with a different meaning and a programming note: "This bit should be programmed to zero (0h) at all times."
Also, I could not find any workaround documented anywhere recommending this bit to be set.
So, I would not recommend to use it in any product, even downstream. Regardless the state of sample c message optimization in later platforms.
Thanks, Rodrigo.
On Tue, May 04, 2021 at 08:07:14PM -0300, André Almeida wrote:
Hi there,
While browsing an old downstream kernel, I found a patch[0] that enables sample_c optimizations at Broadwell GPUs. The message from the upstream commit that enables it for Haswell[1] (and presumably where the code at[0] was copied from) states that "[..] later platforms remove this bit, and apparently always enable the optimization".
Could you confirm that Broadwell and following architectures enable this optimization by default (and thus, patch[0] is a no-op), or should I upstream it?
Thanks, André
[0] https://github.com/ValveSoftware/steamos_kernel/commit/198990f13e1d9429864c1...
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...