From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Pinchart Date: Fri, 14 Aug 2015 23:42:21 +0000 Subject: Re: Issues with rcar-dmac and sh-sci Message-Id: <1862788.NYkJDoIfhG@avalon> List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-sh@vger.kernel.org Hi Geert, On Thursday 16 July 2015 20:36:49 Geert Uytterhoeven wrote: > Hi Laurent, > > While working on DMA for R-Car Gen2 using the sh-sci serial driver with > rcar-dmac, I ran into two issues: > > 1. Unlike the old shdmac DMA engine driver, the new rcar-dmac DMA > engine driver does not support resubmitting a DMA descriptor. > I first tried the patch below, until I ran into the race condition, > after which I changed sh-sci to not reuse DMA descriptors. Is reusing descriptors something that the DMA engine API explicitly allows ? > 2. rcar_dmac_chan_get_residue() has: > > static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan, > dma_cookie_t cookie) > { > struct rcar_dmac_desc *desc = chan->desc.running; > ... > > /* > * If the cookie doesn't correspond to the currently running > transfer * then the descriptor hasn't been processed yet, and the residue > is * equal to the full descriptor size. > */ > if (cookie != desc->async_tx.cookie) > return desc->size; > > If the cookie doesn't correspond to the currently running transfer, > it returns the full descriptor size of the _currently running > transfer_, not the transfer the cookie corresponds to. How about the following (untested) patch ? >From 131968befd5de3400631b879b1574beea27b8239 Mon Sep 17 00:00:00 2001 From: Laurent Pinchart Date: Sat, 15 Aug 2015 01:28:28 +0300 Subject: [PATCH] dmaengine: rcar-dmac: Fix residue reporting for pending descriptors Cookies corresponding to pending transfers have a residue value equal to the full size of the corresponding descriptor. The driver miscomputes that and uses the size of the active descriptor instead. Fix it. Reported-by: Geert Uytterhoeven Signed-off-by: Laurent Pinchart --- drivers/dma/sh/rcar-dmac.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c index 7820d07e7bee..a98596a1f12f 100644 --- a/drivers/dma/sh/rcar-dmac.c +++ b/drivers/dma/sh/rcar-dmac.c @@ -1143,19 +1143,43 @@ static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan, struct rcar_dmac_desc *desc = chan->desc.running; struct rcar_dmac_xfer_chunk *running = NULL; struct rcar_dmac_xfer_chunk *chunk; + enum dma_status status; unsigned int residue = 0; unsigned int dptr = 0; if (!desc) return 0; + + /* + * If the cookie corresponds to a descriptor that has been completed + * there is no residue. The same check has already been performed by the + * caller but without holding the channel lock, so the descriptor could + * now be complete. + */ + status = dma_cookie_status(&chan->chan, cookie, NULL); + if (status = DMA_COMPLETE) + return 0; + /* * If the cookie doesn't correspond to the currently running transfer * then the descriptor hasn't been processed yet, and the residue is * equal to the full descriptor size. */ - if (cookie != desc->async_tx.cookie) - return desc->size; + if (cookie != desc->async_tx.cookie) { + list_for_each_entry(desc, &chan->desc.pending, node) { + if (cookie = desc->async_tx.cookie) + return desc->size; + } + + /* + * No descriptor found for the cookie, there's thus no residue. + * This shouldn't happen if the calling driver passes a correct + * cookie value. + */ + WARN(1, "No descriptor for cookie!"); + return 0; + } /* * In descriptor mode the descriptor running pointer is not maintained > I believe this the reason why the sh-sci driver once thought DMA > transfered 4294967265 (= -31) bytes (for SCIF, descriptor lengths > are either 1 or 32 bytes, and (length) 1 - (residue) 32 > (transfered) -31). > > Thanks for your comments! > > From 589dbd908a59dba6efc2a78fca24645962235ec2 Mon Sep 17 00:00:00 2001 > From: Geert Uytterhoeven > Date: Tue, 14 Jul 2015 11:27:14 +0200 > Subject: [PATCH] [RFC] dmaengine: rcar-dmac: Allow resubmission of DMA > descriptors > > Unlike the old shdmac DMA engine driver, the new rcar-dmac DMA engine > driver does not support resubmitting a DMA descriptor. If a DMA slave > resubmits a descriptor, the descriptor will be added to the "pending > list", while it wasn't removed from the "wait" list. This will cause > list corruption, leading to an infinite loop in > rcar_dmac_chan_reinit(). > > Find out if the descriptor is reused by looking at the current cookie > valie, and remove it from the other list if needed: > - cookie is initialized to -EBUSY (by rcar-dma) for fresh and properly > recycled descriptors, > - cookie is set to a strict-positive value by dma_cookie_assign() (in > core dmaengine code) on submission, > - cookie is reset to zero by dma_cookie_complete() (in core dmaengine > code) on completion, > > Fix this by removing it from a list if the cookie is not -EBUSY. > > FIXME Unfortunately this is racy: the recycled descriptors are not part > of a list while the DMA descriptor callback is running. > > Signed-off-by: Geert Uytterhoeven > --- > drivers/dma/sh/rcar-dmac.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c > index 11e5003a6cc27b40..92a8fddb025e6729 100644 > --- a/drivers/dma/sh/rcar-dmac.c > +++ b/drivers/dma/sh/rcar-dmac.c > @@ -437,8 +437,20 @@ static dma_cookie_t rcar_dmac_tx_submit(struct > dma_async_tx_descriptor *tx) unsigned long flags; > dma_cookie_t cookie; > > + > spin_lock_irqsave(&chan->lock, flags); > > + if (desc->async_tx.cookie != -EBUSY) { > + /* > + * If the descriptor is reused, it's currently part of a list. > + * Hence it must be removed from that list first, before it can > + * be added to the list of pending requests. > + */ > + dev_dbg(chan->chan.device->dev, "chan%u: resubmit active desc %p\n", > + chan->index, desc); > + list_del(&desc->node); > + } > + > cookie = dma_cookie_assign(tx); > > dev_dbg(chan->chan.device->dev, "chan%u: submit #%d@%p\n", -- Regards, Laurent Pinchart