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Date: Thu, 24 Mar 2022 12:55:35 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Yann Gautier <yann.gautier@...s.st.com>
Cc: Christophe Kerello <christophe.kerello@...s.st.com>,
Ludovic Barre <ludovic.barre@...s.st.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Philipp Zabel <p.zabel@...gutronix.de>,
Linus Walleij <linus.walleij@...aro.org>,
linux-mmc@...r.kernel.org,
linux-stm32@...md-mailman.stormreply.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mmc: mmci: stm32: use a buffer for unaligned DMA requests
On Thu, 17 Mar 2022 at 12:19, Yann Gautier <yann.gautier@...s.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@...s.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;
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?
> + }
> } 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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