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Subject: Re: [PATCH v4 03/11] mmc: sdhci: add support for using external DMA
 devices
To:     Peter Ujfalusi <peter.ujfalusi@ti.com>,
        Baolin Wang <baolin.wang7@gmail.com>
CC:     <linux-omap@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        <devicetree@vger.kernel.org>,
        linux-mmc <linux-mmc@vger.kernel.org>, <kishon@ti.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        <mark.rutland@arm.com>, <robh+dt@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>, <tony@atomide.com>
References: <20200106110133.13791-1-faiz_abbas@ti.com>
 <20200106110133.13791-4-faiz_abbas@ti.com>
 <CADBw62onwxPmn=HmdL05hz+FOUe9crRPDO+CB5hDmaVeYMSTsQ@mail.gmail.com>
 <48c10fdf-f2c7-a719-2f64-0f87895f3704@ti.com>
 <CADBw62rK1a9K7cxf5ti7YkFsJJ5tJ+8yjuF2aYR3PnZnoK-r2g@mail.gmail.com>
 <f599735e-83f7-5afc-ebe6-168f0157d2c3@ti.com>
From:   Faiz Abbas <faiz_abbas@ti.com>
Message-ID: <e80a051c-0095-dac0-2e2c-d994ffbf536c@ti.com>
Date:   Fri, 10 Jan 2020 18:46:43 +0530
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Hi Peter,

On 08/01/20 7:05 pm, Peter Ujfalusi wrote:
> Hi,
> 
> On 08/01/2020 11.29, Baolin Wang wrote:
>> Hi Faiz,
>>
>> On Wed, Jan 8, 2020 at 5:19 PM Faiz Abbas <faiz_abbas@ti.com> wrote:
>>>
>>> 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@ti.com> wrote:
>>>>>
>>>>> From: Chunyan Zhang <zhang.chunyan@linaro.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@ti.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@linaro.org>
>>>>> Signed-off-by: Faiz Abbas <faiz_abbas@ti.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?
>>
>> Yes, now it did the same thing. But in future if the DMA engine expand
>> the cookie indication, which may break your current condition, but use
>> dma_submit_error() is more safe, that will help to cover the internal
>> cookie things. So I recommend to use the standard API as far as
>> possible.
> 
> dma_cookie_t is typedefed to s32 currently, but it could change. The
> cookie is for DMA engine internal tracking.
> Clients should not use it directly for doing arithmetic on it.
> 

In that case, I'll fix it with correct API.

Thanks,
Faiz