From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ulf Hansson Subject: Re: [PATCH] mmc: core: Lower max_seg_size if too high for DMA Date: Tue, 11 Dec 2018 14:39:11 +0100 Message-ID: References: <20181031155738.18367-1-tony@atomide.com> <20181129191332.GY53235@atomide.com> <20181211131336.GD9507@n2100.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181211131336.GD9507@n2100.armlinux.org.uk> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Russell King Cc: Tony Lindgren , "linux-mmc@vger.kernel.org" , Kishon , Peter Ujfalusi , linux-omap , Linux ARM List-Id: linux-omap@vger.kernel.org On Tue, 11 Dec 2018 at 14:13, Russell King - ARM Linux wrote: > > On Thu, Nov 29, 2018 at 09:11:17PM +0100, Ulf Hansson wrote: > > On Thu, 29 Nov 2018 at 20:13, Tony Lindgren wrote: > > > > > > * Ulf Hansson [181119 12:09]: > > > > On 31 October 2018 at 16:57, Tony Lindgren wrote: > > > > > With CONFIG_DMA_API_DEBUG_SG a device may produce the following warning: > > > > > > > > > > "DMA-API: mapping sg segment longer than device claims to support" > > > > > > > > > > We default to 64KiB if a DMA engine driver does not initialize dma_parms > > > > > and call dma_set_max_seg_size(). This may be lower that what many MMC > > > > > drivers do with mmc->max_seg_size = mmc->max_blk_size * mmc->max_blk_count. > > > > > > > > > > Let's do a sanity check for max_seg_size being higher than what DMA > > > > > supports in mmc_add_host() and lower it as needed. > > > > > > > > > > Cc: Kishon Vijay Abraham I > > > > > Cc: Peter Ujfalusi > > > > > Cc: Russell King > > > > > Reported-by: Russell King > > > > > Signed-off-by: Tony Lindgren > > > > > --- > > > > > drivers/mmc/core/host.c | 16 ++++++++++++++++ > > > > > 1 file changed, 16 insertions(+) > > > > > > > > > > diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c > > > > > --- a/drivers/mmc/core/host.c > > > > > +++ b/drivers/mmc/core/host.c > > > > > @@ -13,6 +13,7 @@ > > > > > */ > > > > > > > > > > #include > > > > > +#include > > > > > #include > > > > > #include > > > > > #include > > > > > @@ -415,6 +416,19 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev) > > > > > > > > > > EXPORT_SYMBOL(mmc_alloc_host); > > > > > > > > > > +static void mmc_check_max_seg_size(struct mmc_host *host) > > > > > +{ > > > > > + unsigned int max_seg_size = dma_get_max_seg_size(mmc_dev(host)); > > > > > > > > Is dma_get_max_seg_size() really intended to be called for any struct > > > > device (representing the mmc controller) like this? > > > > > > > > My understanding is that the dma_get_max_seg_size() is supposed to be > > > > called by using the DMA engine device, no? > > > > > > Oh good catch sounds like I'm calling it for the wrong device, > > > need to check. In that case sounds like this can't be generic? > > > > No, I don't think so as it's only the mmc host driver that knows about > > the DMA engine device. > > We're nearing the merge window, and this is a regression that is yet > to be solved. It causes a kernel warning with backtrace, so it's > very annoying. > > The error is: > > omap-dma-engine 4a056000.dma-controller: DMA-API: mapping sg segment longer than device claims to support [len=69632] [max=65536] > > which indicates that we have a SG segment length that exceeds thte > published maximum segment size for a device - in this case the > DMA engine device. The maximum segment size for the DMA engine comes > from the default per-device setting, in linux/dma-mapping.h, which is > 64K. > > However, omap_hsmmc sets: > > mmc->max_blk_size = 512; /* Block Length at max can be 1024 */ > mmc->max_blk_count = 0xFFFF; /* No. of Blocks is 16 bits */ > mmc->max_req_size = mmc->max_blk_size * mmc->max_blk_count; > mmc->max_seg_size = mmc->max_req_size; > > which ends up telling the block layer that we support a maximum segment > size of 65535*512, so of course it _will_ pass SG lists where a segment > is longer than 64K. > > The problem here is that the HSMMC driver doesn't take account of the > DMA engine device's capabilities. > > We have something of an odd situation in that the omap-dma device's > maximum SG size depends on the "address width" - it's 64K transfers > of whatever unit "address width" is, so the current implementation of > per-device parameters doesn't exactly work. That means the default > 64K limit at the device-level is reasonable. > > The only thing I can think of doing is adding into omap_hsmmc: > > mmc->max_seg_size = min(mmc->max_req_size, > min(dma_get_max_seg_size(host->rx_chan->device->dev), > dma_get_max_seg_size(host->tx_chan->device->dev))); > > to limit the maximum segment size to that of the device _and_ dma > engine's capabilities. > > Doing this solves the problem for me. Thanks for the suggestion - it sounds like a reasonable way to fix the problem, at least for now. Do you want to send to patch or do you expect someone else to do it? Kind regards Uffe