linux-kernel - Re: [PATCH 4.18 222/235] drm/amd/pp: Send khz clock values to DC for smu7/8

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Message-ID: <86281b7c-8940-5d1b-e164-187087519dc8@amd.com>
Date:   Tue, 9 Oct 2018 09:16:42 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        Sasha Levin <sashal@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "Zhu, Rex" <Rex.Zhu@....com>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: Re: [PATCH 4.18 222/235] drm/amd/pp: Send khz clock values to DC for
 smu7/8

On 2018-10-08 12:17 PM, Deucher, Alexander wrote:
>> -----Original Message-----
>> From: Sasha Levin <sashal@...nel.org>
>> Sent: Monday, October 8, 2018 10:49 AM
>> To: Deucher, Alexander <Alexander.Deucher@....com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>; linux-
>> kernel@...r.kernel.org; stable@...r.kernel.org; Wentland, Harry
>> <Harry.Wentland@....com>; Zhu, Rex <Rex.Zhu@....com>; Sasha Levin
>> <alexander.levin@...rosoft.com>
>> Subject: Re: [PATCH 4.18 222/235] drm/amd/pp: Send khz clock values to DC
>> for smu7/8
>>
>> On Mon, Oct 08, 2018 at 02:33:56PM +0000, Deucher, Alexander wrote:
>>>> -----Original Message-----
>>>> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>> Sent: Monday, September 24, 2018 7:53 AM
>>>> To: linux-kernel@...r.kernel.org
>>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>;
>>>> stable@...r.kernel.org; Wentland, Harry <Harry.Wentland@....com>;
>>>> Deucher, Alexander <Alexander.Deucher@....com>; Zhu, Rex
>>>> <Rex.Zhu@....com>; Sasha Levin <alexander.levin@...rosoft.com>
>>>> Subject: [PATCH 4.18 222/235] drm/amd/pp: Send khz clock values to DC
>>>> for
>>>> smu7/8
>>>>
>>>> 4.18-stable review patch.  If anyone has any objections, please let me
>> know.
>>>>
>>>
>>> This regresses power usage on 4.18.  Please revert.
>>> https://bugzilla.kernel.org/show_bug.cgi?id=201275
>>
>> Hi Alex,
>>
>> Thank you for the report.
>>
>> I'm working on improving this process, I'd be very grateful if you could
>> answer a few questions about this:
>>
>> 1. Is the same breakage seen upstream? (if so, it should be reverted there as
>> well and we can grab the revert into -stable).
> 
> No regression in 4.19 or -next.
> 
>> 2. Does the issue reported by this patch ("pipes seem to hang with a 4k DP
>> and 1080p HDMI display") exist in the 4.18 stable tree?
> 
> I don't think so, but I'm not 100% sure.  Harry, Rex do you know if this is a general issue or was it just fall out from the changes to the interface?
> 

It was intended to deal with fallout to smu7/8 caused by the change to move the kHz-to-10kHz-conversion from display to powerplay. I believe that conversion initially overlooked these blocks. Rex, please correct me if I'm wrong. You probably know more about this than I do.

So yes, I agree, it was never intended to be used without the change to drop the *10 in display code, which was done with this change:

commit 23ec3d1479fd79658cd52c47618d8ddd2f32550b
Author: Rex Zhu <Rex.Zhu@....com>
Date:   Mon Jun 18 18:15:15 2018 +0800

    drm/amd/pp: Convert clock unit to KHz as defined
    
    Convert clock unit 10KHz to KHz as the data sturct defined.
    e.g.
    struct pp_clock_with_latency {
            uint32_t clocks_in_khz;
            uint32_t latency_in_us;
    };
    Meanwhile revert the same conversion in display side.
    
    Acked-by: Alex Deucher <alexander.deucher@....com>
    Acked-by: Harry Wentland <harry.wentland@....com>
    Signed-off-by: Rex Zhu <Rex.Zhu@....com>
    Signed-off-by: Alex Deucher <alexander.deucher@....com>

I don't see this change in the 4.18.y stable tree. I probably should've caught that with the initial 4.18-stable review patch.

Harry

>> 3. If not, could you briefly explain why?
> 
> We refactored the interface between the power and display components and this patch fixed up some of that fallout due to the differences in units used in each component.
> 
>>
>>
>> The algorithm I use was very confident about this patch being stable material,
>> and when I looked at it back then (and again now) I was very confident of the
>> same. If I can understand where I was wrong I could improve my process.
> 
> There are some other dependent patches required that were not flagged in the patch itself.  IIRC, they were a bit big for stable.
> 
> Alex
>