From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from ns.lynxeye.de ([87.118.118.114] helo=lynxeye.de) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1YgTIb-0007q1-PH for barebox@lists.infradead.org; Fri, 10 Apr 2015 07:24:22 +0000 Message-ID: <1428650609.2182.7.camel@lynxeye.de> From: Lucas Stach Date: Fri, 10 Apr 2015 09:23:29 +0200 In-Reply-To: <1428627714-17077-4-git-send-email-sebastian.hesselbarth@gmail.com> References: <1428627714-17077-1-git-send-email-sebastian.hesselbarth@gmail.com> <1428627714-17077-4-git-send-email-sebastian.hesselbarth@gmail.com> Mime-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH 3/4] net: mvneta: Remove unnecessary DMA ops To: Sebastian Hesselbarth Cc: Thomas Petazzoni , barebox@lists.infradead.org Am Freitag, den 10.04.2015, 03:01 +0200 schrieb Sebastian Hesselbarth: > Commit a76c62f80d95860e6c5904ab5cb91667c43f61eb > ("net: mvneta: convert to streaming DMA ops") > converted explicit ARM cache flushes to streaming DMA calls. > > However, in mvneta_send() we are not interested in the sent data buffer > anymore. Also, in mvneta_recv() the device does not care about received > data buffer. > > Remove unnecessary dma_sync_single_for_cpu() in mvneta_send() and > dma_sync_single_for_device() in mvneta_recv(). > > Signed-off-by: Sebastian Hesselbarth NACK: see below. > --- > Cc: barebox@lists.infradead.org > Cc: Lucas Stach > Cc: Ezequiel Garcia > Cc: Thomas Petazzoni > --- > drivers/net/mvneta.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/drivers/net/mvneta.c b/drivers/net/mvneta.c > index 3be2ec531fb1..e1c7f15210e4 100644 > --- a/drivers/net/mvneta.c > +++ b/drivers/net/mvneta.c > @@ -409,7 +409,6 @@ static int mvneta_send(struct eth_device *edev, void *data, int len) > * the Tx port status register (PTXS). > */ > ret = wait_on_timeout(TRANSFER_TIMEOUT, !mvneta_pending_tx(priv)); > - dma_sync_single_for_cpu((unsigned long)data, len, DMA_TO_DEVICE); This makes sure the CPU has a consistent view of memory. If something got speculatively loaded into the cache you will write out invalid data on the next send. > if (ret) { > dev_err(&edev->dev, "transmit timeout\n"); > return ret; > @@ -468,9 +467,6 @@ static int mvneta_recv(struct eth_device *edev) > rxdesc->data_size - MVNETA_MH_SIZE); > ret = 0; > > - dma_sync_single_for_device((unsigned long)rxdesc->buf_phys_addr, > - ALIGN(PKTSIZE, 8), DMA_FROM_DEVICE); > - The buffer is reused for the next receive operation. This isn't syncing the data to the device, but is actually a cache invalidate to make sure there is no pending cache writeback that may corrupt your received data. > recv_err: > /* reset this and get next rx descriptor*/ > rxdesc->data_size = 0; The DMA API has a notion of buffer ownership. Accessing a buffer without transferring the ownership to the appropriate entity (cpu or device) is illegal. Using the DMA API in a non balanced manner is skipping the ownership transfer. Regards, Lucas _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox