linux-kernel - Re: [PATCH 6/6] ARM: da850: adjust memory settings for tilcdc

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Date:   Mon, 3 Oct 2016 10:13:25 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Sekhar Nori <nsekhar@...com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
CC:     Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 6/6] ARM: da850: adjust memory settings for tilcdc

On 10/01/16 12:24, Sekhar Nori wrote:
>> That's good to hear, but I think the priorities should be set:
>> LCDC and EDMA30TC1 to highest priority
>> EDMA30TC0 to priority 2
>>
>> The 0TC0 is used by MMC and if you want to play a video you might need the
>> servicing TC to be higher priority then other masters.
>>
>> If audio playback would trigger sync losts in lcdc then we might need to move
>> 0TC1 to priority 1.
>>
>> I agree that LCDC priority needs to be higher, but I do wonder why the default
>> (5) is not working and if it is not working why it is 5...
>>
>> My guess is that the change in the PBBPR register is the one actually helping
>> here.
> 
> Good point, Peter. If you are booting off NFS and not playing any audio,
> then there is pretty much no EDMA generated traffic on the interconnect.

Yes, this is my understanding as well.

> I would guess too that its the PBBPR setting that is making a
> difference. The EDMA vs LCDC priority adjustment might be needed in
> particular situations too, but specific experiments should be done to
> narrow down on that being the cause.

True, we can use some conservative values for the priority, but the PBBPR
register for sure needs to be updated.

> In any case, to configure the PBBR, you will have to introduce a driver
> for it in drivers/memory. Then you can set it up per board using a DT
> parameter.

and we can reuse the introduced bindings for am335x and OMAP1/2 as well. On
OMAP the legacy DMA API provided a call to raise the priority of the sDMA in
EMIF :o That needs to be removed and replaced.

-- 
Péter