linux-kernel - Re: [PATCH] Revert "dmaengine: pl330: add DMA

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Message-ID: <20180503163521.GZ6014@localhost>
Date:   Thu, 3 May 2018 22:05:22 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Frank Mori Hess <fmh6jj@...il.com>
Cc:     Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        r.baldyga@...kerion.com
Subject: Re: [PATCH] Revert "dmaengine: pl330: add DMA_PAUSE feature"

On Sat, Apr 28, 2018 at 05:50:58PM -0400, Frank Mori Hess wrote:
> This reverts commit 88987d2c7534a0269f567fb101e6d71a08f0f01d.
> 
> The pl330.c pause implementation violates the dmaengine requirement
> for no data loss, since it relies on the DMAKILL
> instruction.  However, DMAKILL discards in-flight data from the
> dma controller's fifo.  This is documented in the dma-330 manual
> and I have observed it with hardware doing device-to-memory burst
> transfers.  The discarded data may or may not show up in the
> residue count, depending on timing (resulting in data corruption
> effectively).


Applied, thanks

-- 
~Vinod