[Intel-gfx] [PATCH] Defined NM doesn't work on KBL and uses automatic N/M.

[Jani Nikula]

On Fri, 26 May 2017, "Wang, Quanxian" <quanxian.wang at intel.com> wrote:
> "The patch is probably fine. But I can't invent an explanation if I
> don't know what the problem is."
>
> @Jani @libin, is it possible for you to help contact Intel graphics
> hardware design engineer to get the reason why M/N doesn't work as you
> implemented in kernel code in Kabylake platform? I don't find good
> reason in bspec. Thanks.

How did you come up with the patch then? What made you try this?

BR,
Jani.


>
> -----Original Message-----
> From: Jani Nikula [mailto:jani.nikula at linux.intel.com] 
> Sent: Friday, May 26, 2017 7:01 PM
> To: Wang, Quanxian <quanxian.wang at intel.com>; intel-gfx at lists.freedesktop.org
> Cc: Yang, Libin <libin.yang at intel.com>
> Subject: RE: [PATCH] Defined NM doesn't work on KBL and uses automatic N/M.
>
> On Fri, 26 May 2017, "Wang, Quanxian" <quanxian.wang at intel.com> wrote:
>> [Wang, Quanxian] in Ubuntu 17.04, we do audio testing on KBL/SKL/APL 
>> and more, the audio doesn't work on KBL specially, and other platform 
>> works fine. Even if with latest upstream kernel, but it works on 4.8 
>> kernel. Therefore It is a regression issue. After investigation, we 
>> found it is caused by commit 
>> "6014ac122ed081feca99217bc57b2e15c7fc1a51] drm/i915/audio: set proper 
>> N/M in modeset". Therefore I provided this patch.
>
> If it's a regression, we need to backport the fix to stable kernels, and the patch needs annotation:
>
> Fixes: 6014ac122ed0 ("drm/i915/audio: set proper N/M in modeset")
> Cc: <stable at vger.kernel.org> # v4.10+
>
>> After getting suggestion from you and Libin, we do more testing on 4K 
>> monitor for audio delay issue. Also talked with Libin why not use 
>> transcoder disable/enable process described in bspec, it will affect 
>> performance.
>>
>> This is the whole story. You can check LCK number 3791 in Intel JIRA 
>> about that.
>
> Actually, I can't. And the commit message needs to have the explanation. I still do not know what the bug is specifically, or why Kabylake, and only Kabylake, needs this.
>
>> [Wang, Quanxian] Basically if upstream could provide a reasonable 
>> patch, it will appreciate since you are expert in this area.
>> Thanks for your understanding.
>
> The patch is probably fine. But I can't invent an explanation if I don't know what the problem is.
>
>
> BR,
> Jani.
>
> --
> Jani Nikula, Intel Open Source Technology Center

-- 
Jani Nikula, Intel Open Source Technology Center