From: Lars-Peter Clausen <lars@metafoo.de>
To: Stephen Warren <swarren@wwwdotorg.org>
Cc: Christopher Freeman <cfreeman@nvidia.com>,
ldewangan@nvidia.com, swarren@nvidia.com, vinod.koul@intel.com,
dan.j.williams@intel.com, dmaengine@vger.kernel.org,
linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 3/3] dma: tegra: avoid int overflow for transferred count
Date: Wed, 07 May 2014 21:15:39 +0200 [thread overview]
Message-ID: <536A865B.1060007@metafoo.de> (raw)
In-Reply-To: <536A61A3.3050601@wwwdotorg.org>
On 05/07/2014 06:38 PM, Stephen Warren wrote:
> On 05/06/2014 03:22 PM, Christopher Freeman wrote:
>> bytes_transferred will overflow during long audio playbacks. Since
>> the driver only ever consults this value modulo bytes_requested, store the
>> value modulo bytes_requested.
>
> The audio driver may only interpret the value modulo bytes_requested,
> but what about other drivers such as the high-speed UART (and SPI?) drivers?
>
> What is the dmaengine API's design requirement here, and what do other
> dmaengine drivers do. If it's to store the modulo, then I'm fine with
> this change.
Yep, this part of the API. The residue should be between transfer length and
0. While 0 is special and should only be returned if the transfer has
finished. For cyclic transfers this means it should never be zero. So if
transferred_bytes is incremented modulo length and residue is length -
transferred_bytes you get the correct result.
next prev parent reply other threads:[~2014-05-07 19:15 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-06 21:22 [PATCH v1 0/3] Tegra DMA residue improvements Christopher Freeman
2014-05-06 21:22 ` [PATCH v1 1/3] dma: tegra: finer granularity residual for tx_status Christopher Freeman
2014-05-07 16:37 ` Stephen Warren
2014-05-07 22:37 ` Christopher Freeman
2014-05-12 17:27 ` Stephen Warren
2014-05-21 6:00 ` Vinod Koul
2014-05-06 21:22 ` [PATCH v1 2/3] dma: tegra: change interrupt-related log levels Christopher Freeman
2014-05-06 21:22 ` [PATCH v1 3/3] dma: tegra: avoid int overflow for transferred count Christopher Freeman
2014-05-07 16:38 ` Stephen Warren
2014-05-07 19:15 ` Lars-Peter Clausen [this message]
2014-05-07 22:50 ` Christopher Freeman
2014-05-07 6:38 ` [PATCH v1 0/3] Tegra DMA residue improvements Lars-Peter Clausen
2014-05-07 21:27 ` Christopher Freeman
2014-05-21 5:52 ` Vinod Koul
2014-05-21 6:58 ` Lars-Peter Clausen
2014-05-21 11:06 ` Vinod Koul
2014-05-21 16:21 ` Stephen Warren
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