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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Thu, 26 Mar 2020 12:01:28 +0100
Message-ID: <CACRpkdbFQ4kjgxxwrTjXZWAt38AM2kyMbeaCX6wjMgyyRmE55Q@mail.gmail.com>
Subject: Re: [PATCH 1/2] driver core: platform: Initialize dma_parms for
 platform devices
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Christoph Hellwig <hch@lst.de>,
        Russell King <linux@armlinux.org.uk>,
        Vinod Koul <vkoul@kernel.org>, Haibo Chen <haibo.chen@nxp.com>,
        Ludovic Barre <ludovic.barre@st.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        dmaengine <dmaengine@vger.kernel.org>,
        stable <stable@vger.kernel.org>
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On Wed, Mar 25, 2020 at 12:34 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:

> It's currently the platform driver's responsibility to initialize the
> pointer, dma_parms, for its corresponding struct device. The benefit with
> this approach allows us to avoid the initialization and to not waste memory
> for the struct device_dma_parameters, as this can be decided on a case by
> case basis.
>
> However, it has turned out that this approach is not very practical.  Not
> only does it lead to open coding, but also to real errors. In principle
> callers of dma_set_max_seg_size() doesn't check the error code, but just
> assumes it succeeds.
>
> For these reasons, let's do the initialization from the common platform bus
> at the device registration point. This also follows the way the PCI devices
> are being managed, see pci_device_add().
>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

This seems in line with what Christoph said.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

I imagine we can eventually set up more of the DMA config such
as segment size based on config from the device tree, but I'm not
sure about that yet.

Yours,
Linus Walleij