Messages in this thread | | | Date | Fri, 25 Mar 2022 15:01:45 +0100 | Subject | Re: [PATCH 2/2] mmc: mmci: stm32: use a buffer for unaligned DMA requests | From | Yann Gautier <> |
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On 3/25/22 14:43, Ulf Hansson wrote: > On Thu, 24 Mar 2022 at 17:23, Yann Gautier <yann.gautier@foss.st.com> wrote: >> >> On 3/24/22 12:55, Ulf Hansson wrote: >>> On Thu, 17 Mar 2022 at 12:19, Yann Gautier <yann.gautier@foss.st.com> wrote: >>>> >>>> In SDIO mode, the sg list for requests can be unaligned with what the >>>> STM32 SDMMC internal DMA can support. In that case, instead of failing, >>>> use a temporary bounce buffer to copy from/to the sg list. >>>> This buffer is limited to 1MB. But for that we need to also limit >>>> max_req_size to 1MB. It has not shown any throughput penalties for >>>> SD-cards or eMMC. >>>> >>>> Signed-off-by: Yann Gautier <yann.gautier@foss.st.com> >>>> --- >>>> drivers/mmc/host/mmci_stm32_sdmmc.c | 80 +++++++++++++++++++++++------ >>>> 1 file changed, 63 insertions(+), 17 deletions(-) >>>> >>>> diff --git a/drivers/mmc/host/mmci_stm32_sdmmc.c b/drivers/mmc/host/mmci_stm32_sdmmc.c >>>> index 4566d7fc9055..a4414e32800f 100644 >>>> --- a/drivers/mmc/host/mmci_stm32_sdmmc.c >>>> +++ b/drivers/mmc/host/mmci_stm32_sdmmc.c >>>> @@ -43,6 +43,9 @@ struct sdmmc_lli_desc { >>>> struct sdmmc_idma { >>>> dma_addr_t sg_dma; >>>> void *sg_cpu; >>>> + dma_addr_t bounce_dma_addr; >>>> + void *bounce_buf; >>>> + bool use_bounce_buffer; >>>> }; >>>> >>>> struct sdmmc_dlyb { >>>> @@ -54,6 +57,7 @@ struct sdmmc_dlyb { >>>> static int sdmmc_idma_validate_data(struct mmci_host *host, >>>> struct mmc_data *data) >>>> { >>>> + struct sdmmc_idma *idma = host->dma_priv; >>>> struct scatterlist *sg; >>>> int i; >>>> >>>> @@ -61,21 +65,23 @@ static int sdmmc_idma_validate_data(struct mmci_host *host, >>>> * idma has constraints on idmabase & idmasize for each element >>>> * excepted the last element which has no constraint on idmasize >>>> */ >>>> + idma->use_bounce_buffer = false; >>>> for_each_sg(data->sg, sg, data->sg_len - 1, i) { >>>> if (!IS_ALIGNED(sg->offset, sizeof(u32)) || >>>> !IS_ALIGNED(sg->length, SDMMC_IDMA_BURST)) { >>>> - dev_err(mmc_dev(host->mmc), >>>> + dev_dbg(mmc_dev(host->mmc), >>>> "unaligned scatterlist: ofst:%x length:%d\n", >>>> data->sg->offset, data->sg->length); >>>> - return -EINVAL; >>>> + idma->use_bounce_buffer = true; >>>> + return 0; >>>> } >>>> } >>>> >>>> if (!IS_ALIGNED(sg->offset, sizeof(u32))) { >>>> - dev_err(mmc_dev(host->mmc), >>>> + dev_dbg(mmc_dev(host->mmc), >>>> "unaligned last scatterlist: ofst:%x length:%d\n", >>>> data->sg->offset, data->sg->length); >>>> - return -EINVAL; >>>> + idma->use_bounce_buffer = true; >>>> } >>>> >>>> return 0; >>>> @@ -84,18 +90,29 @@ static int sdmmc_idma_validate_data(struct mmci_host *host, >>>> static int _sdmmc_idma_prep_data(struct mmci_host *host, >>>> struct mmc_data *data) >>>> { >>>> - int n_elem; >>>> + struct sdmmc_idma *idma = host->dma_priv; >>>> >>>> - n_elem = dma_map_sg(mmc_dev(host->mmc), >>>> - data->sg, >>>> - data->sg_len, >>>> - mmc_get_dma_dir(data)); >>>> + if (idma->use_bounce_buffer) { >>>> + if (data->flags & MMC_DATA_WRITE) { >>>> + unsigned int xfer_bytes = data->blksz * data->blocks; >>>> >>>> - if (!n_elem) { >>>> - dev_err(mmc_dev(host->mmc), "dma_map_sg failed\n"); >>>> - return -EINVAL; >>>> - } >>>> + sg_copy_to_buffer(data->sg, data->sg_len, >>>> + idma->bounce_buf, xfer_bytes); >>>> + dma_wmb(); >>>> + } >>>> + } else { >>>> + int n_elem; >>>> + >>>> + n_elem = dma_map_sg(mmc_dev(host->mmc), >>>> + data->sg, >>>> + data->sg_len, >>>> + mmc_get_dma_dir(data)); >>>> >>>> + if (!n_elem) { >>>> + dev_err(mmc_dev(host->mmc), "dma_map_sg failed\n"); >>>> + return -EINVAL; >>>> + } >>>> + } >>>> return 0; >>>> } >>>> >>>> @@ -112,8 +129,19 @@ static int sdmmc_idma_prep_data(struct mmci_host *host, >>>> static void sdmmc_idma_unprep_data(struct mmci_host *host, >>>> struct mmc_data *data, int err) >>>> { >>>> - dma_unmap_sg(mmc_dev(host->mmc), data->sg, data->sg_len, >>>> - mmc_get_dma_dir(data)); >>>> + struct sdmmc_idma *idma = host->dma_priv; >>>> + >>>> + if (idma->use_bounce_buffer) { >>>> + if (data->flags & MMC_DATA_READ) { >>>> + unsigned int xfer_bytes = data->blksz * data->blocks; >>>> + >>>> + sg_copy_from_buffer(data->sg, data->sg_len, >>>> + idma->bounce_buf, xfer_bytes); >>>> + } >>>> + } else { >>>> + dma_unmap_sg(mmc_dev(host->mmc), data->sg, data->sg_len, >>>> + mmc_get_dma_dir(data)); >>>> + } >>>> } >>>> >>>> static int sdmmc_idma_setup(struct mmci_host *host) >>>> @@ -137,6 +165,16 @@ static int sdmmc_idma_setup(struct mmci_host *host) >>>> host->mmc->max_segs = SDMMC_LLI_BUF_LEN / >>>> sizeof(struct sdmmc_lli_desc); >>>> host->mmc->max_seg_size = host->variant->stm32_idmabsize_mask; >>>> + >>>> + host->mmc->max_req_size = SZ_1M; >>>> + idma->bounce_buf = dmam_alloc_coherent(dev, >>>> + host->mmc->max_req_size, >>>> + &idma->bounce_dma_addr, >>>> + GFP_KERNEL); >>>> + if (!idma->bounce_buf) { >>>> + dev_err(dev, "Unable to map allocate DMA bounce buffer.\n"); >>>> + return -ENOMEM; >>> >> Hi Ulf, >> >>> If we fail to allocate the 1M bounce buffer, then we end up always >>> using a PIO based mode, right? >>> >>> Perhaps we can allow the above allocation to fail, but then limit us >>> to use DMA only when the buffers are properly aligned? Would that >>> work? >>> >> We have never supported PIO mode with STM32 variant. >> We only support DMA single buffer or DMA LLI. >> As we cannot have DMA LLI for unaligned access, we'll default to single >> mode. > > Right, I was looking at the legacy variant, which uses PIO as > fallback. Sorry for my ignorance. > >> If allocation fails, it then won't work. > > Right, but that's only part of the issue, I think. > >> Maybe we shouldn't fail here, and just check idma->bounce_buf in >> validate data function. If buffer is not allocated, we just return >> -EINVAL as it was done before. > > Yes, something along those lines. However, there is another problem > too, which is that the allocation will be done for each instance of > the host that is probed. In all cases but the SDIO case, this would be > a waste, right? > > Perhaps we should manage the allocation in the validate function too > (de-allocation should be handled at ->remove()). In this way, the > buffer will only be allocated when it's actually needed. Yes, it would > add a latency while serving the *first* request that has unaligned > buffers, but I guess we can live with that? > Hi Ulf,
That makes sense, I'll rework the validate data function with this. I'll push a new version soon.
Thanks, Yann >> >> Best regards, >> Yann > > Kind regards > Uffe > >> >>>> + } >>>> } else { >>>> host->mmc->max_segs = 1; >>>> host->mmc->max_seg_size = host->mmc->max_req_size; >>>> @@ -154,8 +192,16 @@ static int sdmmc_idma_start(struct mmci_host *host, unsigned int *datactrl) >>>> struct scatterlist *sg; >>>> int i; >>>> >>>> - if (!host->variant->dma_lli || data->sg_len == 1) { >>>> - writel_relaxed(sg_dma_address(data->sg), >>>> + if (!host->variant->dma_lli || data->sg_len == 1 || >>>> + idma->use_bounce_buffer) { >>>> + u32 dma_addr; >>>> + >>>> + if (idma->use_bounce_buffer) >>>> + dma_addr = idma->bounce_dma_addr; >>>> + else >>>> + dma_addr = sg_dma_address(data->sg); >>>> + >>>> + writel_relaxed(dma_addr, >>>> host->base + MMCI_STM32_IDMABASE0R); >>>> writel_relaxed(MMCI_STM32_IDMAEN, >>>> host->base + MMCI_STM32_IDMACTRLR); >>> >>> Kind regards >>> Uffe >>
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