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SubjectRe: [PATCH v4 03/11] mmc: sdhci: add support for using external DMA devices
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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

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