Date:   Wed, 8 Jan 2020 14:50:27 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Baolin Wang <baolin.wang7@...il.com>
CC:     <linux-omap@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>, <kishon@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        <mark.rutland@....com>, <robh+dt@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>, <tony@...mide.com>
Subject: Re: [PATCH v4 03/11] mmc: sdhci: add support for using external DMA
 devices

Hi Baolin,

On 08/01/20 6:58 am, Baolin Wang wrote:
> Hi Faiz,
> 
> On Mon, Jan 6, 2020 at 7:01 PM Faiz Abbas <faiz_abbas@...com> wrote:
>>
>> From: Chunyan Zhang <zhang.chunyan@...aro.org>
>>
>> Some standard SD host controllers can support both external dma
>> controllers as well as ADMA/SDMA in which the SD host controller
>> acts as DMA master. TI's omap controller is the case as an example.
>>
>> Currently the generic SDHCI code supports ADMA/SDMA integrated in
>> the host controller but does not have any support for external DMA
>> controllers implemented using dmaengine, meaning that custom code is
>> needed for any systems that use an external DMA controller with SDHCI.
>>
>> Fixes by Faiz Abbas <faiz_abbas@...com>:
>> 1. Map scatterlists before dmaengine_prep_slave_sg()
>> 2. Use dma_async() functions inside of the send_command() path and call
>> terminate_sync() in non-atomic context in case of an error.
>>
>> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
>> Signed-off-by: Faiz Abbas <faiz_abbas@...com>
>> ---
>>  drivers/mmc/host/Kconfig |   3 +
>>  drivers/mmc/host/sdhci.c | 228 ++++++++++++++++++++++++++++++++++++++-
>>  drivers/mmc/host/sdhci.h |   8 ++
>>  3 files changed, 237 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
>> index d06b2dfe3c95..adef971582a1 100644
>> --- a/drivers/mmc/host/Kconfig
>> +++ b/drivers/mmc/host/Kconfig
>> @@ -1040,3 +1040,6 @@ config MMC_OWL
>>         help
>>           This selects support for the SD/MMC Host Controller on
>>           Actions Semi Owl SoCs.
>> +
>> +config MMC_SDHCI_EXTERNAL_DMA
>> +       bool
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index f6999054abcf..8cc78c76bc3d 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -10,6 +10,7 @@
>>   */
>>
>>  #include <linux/delay.h>
>> +#include <linux/dmaengine.h>
>>  #include <linux/ktime.h>
>>  #include <linux/highmem.h>
>>  #include <linux/io.h>
>> @@ -1157,6 +1158,188 @@ static void sdhci_prepare_data(struct sdhci_host *host, struct mmc_command *cmd)
>>         sdhci_set_block_info(host, data);
>>  }
>>
>> +#if IS_ENABLED(CONFIG_MMC_SDHCI_EXTERNAL_DMA)
>> +
>> +static int sdhci_external_dma_init(struct sdhci_host *host)
>> +{
>> +       int ret = 0;
>> +       struct mmc_host *mmc = host->mmc;
>> +
>> +       host->tx_chan = dma_request_chan(mmc->parent, "tx");
>> +       if (IS_ERR(host->tx_chan)) {
>> +               ret = PTR_ERR(host->tx_chan);
>> +               if (ret != -EPROBE_DEFER)
>> +                       pr_warn("Failed to request TX DMA channel.\n");
>> +               host->tx_chan = NULL;
>> +               return ret;
>> +       }
>> +
>> +       host->rx_chan = dma_request_chan(mmc->parent, "rx");
>> +       if (IS_ERR(host->rx_chan)) {
>> +               if (host->tx_chan) {
>> +                       dma_release_channel(host->tx_chan);
>> +                       host->tx_chan = NULL;
>> +               }
>> +
>> +               ret = PTR_ERR(host->rx_chan);
>> +               if (ret != -EPROBE_DEFER)
>> +                       pr_warn("Failed to request RX DMA channel.\n");
>> +               host->rx_chan = NULL;
>> +       }
>> +
>> +       return ret;
>> +}
>> +
>> +static struct dma_chan *sdhci_external_dma_channel(struct sdhci_host *host,
>> +                                                  struct mmc_data *data)
>> +{
>> +       return data->flags & MMC_DATA_WRITE ? host->tx_chan : host->rx_chan;
>> +}
>> +
>> +static int sdhci_external_dma_setup(struct sdhci_host *host,
>> +                                   struct mmc_command *cmd)
>> +{
>> +       int ret, i;
>> +       struct dma_async_tx_descriptor *desc;
>> +       struct mmc_data *data = cmd->data;
>> +       struct dma_chan *chan;
>> +       struct dma_slave_config cfg;
>> +       dma_cookie_t cookie;
>> +       int sg_cnt;
>> +
>> +       if (!host->mapbase)
>> +               return -EINVAL;
>> +
>> +       cfg.src_addr = host->mapbase + SDHCI_BUFFER;
>> +       cfg.dst_addr = host->mapbase + SDHCI_BUFFER;
>> +       cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
>> +       cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
>> +       cfg.src_maxburst = data->blksz / 4;
>> +       cfg.dst_maxburst = data->blksz / 4;
>> +
>> +       /* Sanity check: all the SG entries must be aligned by block size. */
>> +       for (i = 0; i < data->sg_len; i++) {
>> +               if ((data->sg + i)->length % data->blksz)
>> +                       return -EINVAL;
>> +       }
>> +
>> +       chan = sdhci_external_dma_channel(host, data);
>> +
>> +       ret = dmaengine_slave_config(chan, &cfg);
>> +       if (ret)
>> +               return ret;
>> +
>> +       sg_cnt = sdhci_pre_dma_transfer(host, data, COOKIE_MAPPED);
>> +       if (sg_cnt <= 0)
>> +               return -EINVAL;
>> +
>> +       desc = dmaengine_prep_slave_sg(chan, data->sg, data->sg_len,
>> +                                      mmc_get_dma_dir(data),
>> +                                      DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
>> +       if (!desc)
>> +               return -EINVAL;
>> +
>> +       desc->callback = NULL;
>> +       desc->callback_param = NULL;
>> +
>> +       cookie = dmaengine_submit(desc);
>> +       if (cookie < 0)
> 
> We usually use the DMA engine standard API: dma_submit_error() to
> validate the cookie.
> 

The if condition is doing the same thing as the API. Do we really
require it?

Thanks,
Faiz

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