linux-kernel - Re: [PATCH] dmaengine: imx-sdma: fix context cache

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Date:   Wed, 29 Jan 2020 17:19:45 -0300
From:   Fabio Estevam <festevam@...il.com>
To:     Martin Fuzzey <martin.fuzzey@...wbird.group>
Cc:     dmaengine@...r.kernel.org, stable <stable@...r.kernel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Robin Gong <yibin.gong@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dmaengine: imx-sdma: fix context cache

Hi Martin,

Thanks for the fix.

On Wed, Jan 29, 2020 at 10:41 AM Martin Fuzzey
<martin.fuzzey@...wbird.group> wrote:
>
> There is a DMA problem with the serial ports on i.MX6.
>
> When the following sequence is performed:
>
> 1) Open a port
> 2) Write some data
> 3) Close the port
> 4) Open a *different* port
> 5) Write some data
> 6) Close the port
>
> The second write sends nothing and the second close hangs.
> If the first close() is omitted it works.
>
> Adding logs to the the UART driver shows that the DMA is being setup but
> the callback is never invoked for the second write.
>
> This used to work in 4.19.
>
> Git bisect leads to:
>         ad0d92d: "dmaengine: imx-sdma: refine to load context only once"
>
> This commit adds a "context_loaded" flag used to avoid unnecessary context
> setups.
> However the flag is only reset in sdma_channel_terminate_work(),
> which is only invoked in a worker triggered by sdma_terminate_all() IF
> there is an active descriptor.
>
> So, if no active descriptor remains when the channel is terminated, the
> flag is not reset and, when the channel is later reused the old context
> is used.
>
> Fix the problem by always resetting the flag in sdma_free_chan_resources().
>
> Fixes: ad0d92d: "dmaengine: imx-sdma: refine to load context only once"

Nit: in the Fixes tag we use 12 digits for the commit ID and the
Subject is enclosed by parenthesis.

The preferred format would be:

Fixes: ad0d92d7ba6a ("dmaengine: imx-sdma: refine to load context only once")

Reviewed-by: Fabio Estevam <festevam@...il.com>

Thanks