Tony, On 2018-10-31 17:57, 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. I tried to address it with: https://patchwork.kernel.org/patch/9948967/ https://patchwork.kernel.org/patch/9948989/ https://patchwork.kernel.org/patch/9948975/ but it is back in the drawing board for now. The problem is that with eDMA/SDMA the size limit is not bytes, but the number of bursts. Different addr_width and burst combination would result different max_seg_size and I can not guess before the user provide the dma_slave_config via dmaengine_slave_config(). I have experimental patches to modify the max_seg_size of the _channel_ proactively in response slave_config and then we should have an API to query it from the DMA _channel_, not from the DMA device as each channel can have different limit on the max_seg_size. > > Cc: Kishon Vijay Abraham I <kishon@xxxxxx> > Cc: Peter Ujfalusi <peter.ujfalusi@xxxxxx> > Cc: Russell King <rmk+kernel@xxxxxxxxxxxxxxx> > Reported-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx> > Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx> Reviewed-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx> > --- > 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 <linux/device.h> > +#include <linux/dma-mapping.h> > #include <linux/err.h> > #include <linux/idr.h> > #include <linux/of.h> > @@ -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)); > + > + if (host->max_seg_size <= max_seg_size) > + return; > + > + dev_info(mmc_dev(host), "Lowering max_seg_size for DMA: %u vs %u\n", > + host->max_seg_size, max_seg_size); > + > + host->max_seg_size = max_seg_size; > +} > + > /** > * mmc_add_host - initialise host hardware > * @host: mmc host > @@ -430,6 +444,8 @@ int mmc_add_host(struct mmc_host *host) > WARN_ON((host->caps & MMC_CAP_SDIO_IRQ) && > !host->ops->enable_sdio_irq); > > + mmc_check_max_seg_size(host); > + > err = device_add(&host->class_dev); > if (err) > return err; > - Péter Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
