From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: [PATCH] mmc: core: Lower max_seg_size if too high for DMA Date: Tue, 11 Dec 2018 13:49:37 +0000 Message-ID: <20181211134937.GE9507@n2100.armlinux.org.uk> 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: Content-Disposition: inline In-Reply-To: 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: Ulf Hansson Cc: Tony Lindgren , "linux-mmc@vger.kernel.org" , Kishon , Peter Ujfalusi , linux-omap , Linux ARM List-Id: linux-mmc@vger.kernel.org On Tue, Dec 11, 2018 at 02:39:11PM +0100, Ulf Hansson wrote: > 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. I don't think there's any "at least for now" about this approach - it's not something that the MMC core can know about, because whether a driver uses DMA engine or not, and how many channels it uses is completely driver specific. The only questionable thing is around the dma_get_max_seg_size() interface, but the only way that's going to get solved is to eliminate it entirely as it isn't a per-device property with some DMA engines such as omap-dma - it's a per-request property. That also means killing the check in the DMA debug code, which isn't going to go down very well. > Do you want to send to patch or do you expect someone else to do it? I'll send a patch once I've checked the corner cases, and whether we should go further and include other DMA parameters from the dma engine. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9B365C07E85 for ; Tue, 11 Dec 2018 13:50:08 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6B76620849 for ; 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bh=9NMzM5M9pPXUFLDj+J9a4yYEeEsKyctE0Ug8UO1rtnE=; b=FyV8lj3sX48/88CSmGO07l/in sJ+GtMpzkKMMOYV0KT7ZngW12bVHlWAyl0t7DCjBQVmMeLQ2uwryN704+0FYFL+bYLfr+4NOmszAt Y5RJw+uGEz+Ly9GEl3cMyAZDtWLB4A9pUis07wkGIFP7tRtCtnpn/l1w5BX43i3XYYOVM=; Received: from n2100.armlinux.org.uk ([2001:4d48:ad52:3201:214:fdff:fe10:4f86]:57174) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.90_1) (envelope-from ) id 1gWiPu-0006qJ-HQ; Tue, 11 Dec 2018 13:49:42 +0000 Received: from linux by n2100.armlinux.org.uk with local (Exim 4.90_1) (envelope-from ) id 1gWiPr-0008Ub-M3; Tue, 11 Dec 2018 13:49:39 +0000 Date: Tue, 11 Dec 2018 13:49:37 +0000 From: Russell King - ARM Linux To: Ulf Hansson Subject: Re: [PATCH] mmc: core: Lower max_seg_size if too high for DMA Message-ID: <20181211134937.GE9507@n2100.armlinux.org.uk> References: <20181031155738.18367-1-tony@atomide.com> <20181129191332.GY53235@atomide.com> <20181211131336.GD9507@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20181211_055001_386759_854268B6 X-CRM114-Status: GOOD ( 36.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tony Lindgren , "linux-mmc@vger.kernel.org" , Kishon , Peter Ujfalusi , linux-omap , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Dec 11, 2018 at 02:39:11PM +0100, Ulf Hansson wrote: > 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. I don't think there's any "at least for now" about this approach - it's not something that the MMC core can know about, because whether a driver uses DMA engine or not, and how many channels it uses is completely driver specific. The only questionable thing is around the dma_get_max_seg_size() interface, but the only way that's going to get solved is to eliminate it entirely as it isn't a per-device property with some DMA engines such as omap-dma - it's a per-request property. That also means killing the check in the DMA debug code, which isn't going to go down very well. > Do you want to send to patch or do you expect someone else to do it? I'll send a patch once I've checked the corner cases, and whether we should go further and include other DMA parameters from the dma engine. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel