linux-kernel - Re: [PATCH] dmaengine: qcom-bam: fix circular buffer handling

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Message-ID: <20190614194322.GA4791@hector.attlocal.net>
Date:   Fri, 14 Jun 2019 14:43:22 -0500
From:   Andy Gross <agross@...nel.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     vkoul@...nel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        sricharan@...eaurora.org
Subject: Re: [PATCH] dmaengine: qcom-bam: fix circular buffer handling

On Fri, Jun 14, 2019 at 03:20:12PM +0100, Srinivas Kandagatla wrote:
> For some reason arguments to most of the circular buffers
> macros are used in reverse, tail is used for head and vice versa.
> 
> This leads to bam thinking that there is an extra descriptor at the
> end and leading to retransmitting descriptor which was not scheduled
> by any driver. This happens after MAX_DESCRIPTORS (4096) are scheduled
> and done, so most of the drivers would not notice this, unless they are
> heavily using bam dma. Originally found this issue while testing
> SoundWire over SlimBus on DB845c which uses DMA very heavily for
> read/writes.
> 
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>

Reviewed-by: Andy Gross <agross@...nel.org>