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

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Message-ID: <CACRpkdaiOhMGzuWPwoRLZ05HyM8BO_-cZt4TiAqAYQvDaJA-mA@mail.gmail.com>
Date:   Tue, 29 Mar 2022 23:16:51 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Manivannan Sadhasivam <mani@...nel.org>,
        Srini Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     Yann Gautier <yann.gautier@...s.st.com>, ulf.hansson@...aro.org,
        Rob Herring <robh+dt@...nel.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,
        Grzegorz Szymaszek <gszymaszek@...rt.pl>
Subject: Re: [PATCH 1/3] dt-bindings: mmc: mmci: add a property to disable DMA LLI

On Tue, Mar 29, 2022 at 7:33 PM Manivannan Sadhasivam <mani@...nel.org> wrote:
> [Yann]
> > As for Prabhakar's answer, the IDMA here is inside our IP, and not used in
> > any other IP. So I'm not sure it is really relevant to move that to another
> > dmaengine driver.
>
> Okay, I think this justification makes sense. I was worried of DMA IPs that get
> sandwiched into many peripherals like the one on Renesas platforms. It turned
> out that each subsystem has to add internal DMA support for it :/

That is a justified worry.

Qualcomm has "BAM DMA" (I think it is called?) which is added to each IP
that needs DMA. drivers/mmc/host/mmci_qcom_dml.c
It's for older Qualcomm platforms but I *think* it is actually not just used
for the MMCI, just noone ever got around to adding it to any other
peripheral? Srini do you know?

Yours,
Linus Walleij