linux-kernel - Re: [PATCH 1/3] dt-bindings: mmc: mmci: add a property to disable DMA LLI

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Date:   Mon, 28 Mar 2022 16:58:52 +0200
From:   Yann Gautier <yann.gautier@...s.st.com>
To:     Linus Walleij <linus.walleij@...aro.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Christophe Kerello <christophe.kerello@...s.st.com>,
        Ludovic Barre <ludovic.barre@...s.st.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Russell King <linux@...linux.org.uk>,
        Marek Vasut <marex@...x.de>, <kernel@...electronics.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Grzegorz Szymaszek <gszymaszek@...rt.pl>
Subject: Re: [PATCH 1/3] dt-bindings: mmc: mmci: add a property to disable DMA
 LLI

On 3/25/22 21:12, Linus Walleij wrote:
> On Tue, Mar 15, 2022 at 9:26 AM Yann Gautier <yann.gautier@...s.st.com> wrote:
> 
>> The STM32 variant uses an internal DMA, and the DMA functions are in its
>> dedicated file. So I was planning to do the same as what is done in
>> meson-gx-mmc.c: using a bounce buffer to copy from/to in case DMA
>> constraints are not fulfilled. Not sure it can help for Ux500.
>>
>> Ulf, before I send my new series (although it is not ready yet), would
>> you be OK with the bounce buffer idea?
> 
Hi Linus,

> Would it not be better if the bounce buffer is something available
> for all MMCI variants and not restricted to the STM32 DMA add-on?

The issue was seen with the internal DMA of the STM32 variant of PL180.

> 
> What I'm thinking is that this is a problem with the MMCI hardware
> rather than with the DMA hardware, so the problem kind of gets
> fixed in the wrong place if the bounce buffer is in the DMA add-on
> code.
> 
> Maybe this is how you fixed it in later patches, I'll take a look.

I've pushed a new version there to correct latest remarks from Ulf:
https://lore.kernel.org/all/20220328145114.334577-1-yann.gautier@foss.st.com/


> 
> Yours,
> Linus Walleij

Best regards,
Yann