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Date: Mon, 16 Sep 2019 16:17:00 +0200 From: Lucas Stach <l.stach@...gutronix.de> To: Philipp Puschmann <philipp.puschmann@...ix.com>, linux-kernel@...r.kernel.org Cc: linux-serial@...r.kernel.org, shawnguo@...nel.org, s.hauer@...gutronix.de, jslaby@...e.com, vkoul@...nel.org, linux-imx@....com, kernel@...gutronix.de, gregkh@...uxfoundation.org, dmaengine@...r.kernel.org, dan.j.williams@...el.com, festevam@...il.com, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH 1/4] dmaengine: imx-sdma: fix buffer ownership On Mi, 2019-09-11 at 16:49 +0200, Philipp Puschmann wrote: > BD_DONE flag marks ownership of the buffer. When 1 SDMA owns the buffer, > when 0 ARM owns it. When processing the buffers in > sdma_update_channel_loop the ownership of the currently processed buffer > was set to SDMA again before running the callback function of the the > buffer and while the sdma script may be running in parallel. So there was > the possibility to get the buffer overwritten by SDMA before it has been > processed by kernel leading to kind of random errors in the upper layers, > e.g. bluetooth. > > It may be further a good idea to make the status struct member volatile or > access it using writel or similar to rule out that the compiler sets the > BD_DONE flag before the callback routine has finished. > > Signed-off-by: Philipp Puschmann <philipp.puschmann@...ix.com> > --- > drivers/dma/imx-sdma.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c > index a01f4b5d793c..1abb14ff394d 100644 > --- a/drivers/dma/imx-sdma.c > +++ b/drivers/dma/imx-sdma.c > @@ -802,7 +802,6 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac) > */ > > desc->chn_real_count = bd->mode.count; > - bd->mode.status |= BD_DONE; > bd->mode.count = desc->period_len; > desc->buf_ptail = desc->buf_tail; > desc->buf_tail = (desc->buf_tail + 1) % desc->num_bd; > @@ -817,6 +816,8 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac) > dmaengine_desc_get_callback_invoke(&desc->vd.tx, NULL); > spin_lock(&sdmac->vc.lock); To address your comment from the second paragraph of the commit message there should be a dma_wmb() here before changing the status flag. Regards, Lucas > + bd->mode.status |= BD_DONE; > + > if (error) > sdmac->status = old_status; > }
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