Date:   Mon, 28 Jan 2019 18:20:28 +0800
From:   Chunyan Zhang <zhang.chunyan@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Faiz Abbas <faiz_abbas@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, linux-mmc@...r.kernel.org,
        Kishon Vijay Abraham I <kishon@...com>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH 1/7] mmc: sdhci: add support for using external DMA devices

On Thu, 24 Jan 2019 at 19:41, Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> On 11/01/19 1:08 PM, Faiz Abbas 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
> > synchronize once at the start of each request.
>
> Sorry for the slow reply, but I do have some concerns.  Please see the comments.
>
> >
> > 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 | 266 ++++++++++++++++++++++++++++++++++++++-
> >  drivers/mmc/host/sdhci.h |   8 ++
> >  3 files changed, 273 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
> > index e26b8145efb3..333292e8ecdd 100644
> > --- a/drivers/mmc/host/Kconfig
> > +++ b/drivers/mmc/host/Kconfig
> > @@ -999,3 +999,6 @@ config MMC_SDHCI_AM654
> >         If you have a controller with this interface, say Y or M here.
> >
> >         If unsure, say N.
> > +
> > +config MMC_SDHCI_EXTERNAL_DMA
> > +        bool
> > diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> > index a22e11a65658..4a9044c06e21 100644
> > --- a/drivers/mmc/host/sdhci.c
> > +++ b/drivers/mmc/host/sdhci.c
> > @@ -14,6 +14,7 @@
> >   */
> >
> >  #include <linux/delay.h>
> > +#include <linux/dmaengine.h>
> >  #include <linux/ktime.h>
> >  #include <linux/highmem.h>
> >  #include <linux/io.h>
> > @@ -1118,6 +1119,226 @@ static void sdhci_prepare_data(struct sdhci_host *host, struct mmc_command *cmd)
> >       }
> >  }
> >
> > +#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 inline 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)
> > +             ret = cookie;
> > +
> > +     return ret;
> > +}
> > +
> > +static void sdhci_external_dma_release(struct sdhci_host *host)
> > +{
> > +     if (host->tx_chan) {
> > +             dma_release_channel(host->tx_chan);
> > +             host->tx_chan = NULL;
> > +     }
> > +
> > +     if (host->rx_chan) {
> > +             dma_release_channel(host->rx_chan);
> > +             host->rx_chan = NULL;
> > +     }
> > +
> > +     sdhci_switch_external_dma(host, false);
> > +}
> > +
> > +static int __sdhci_external_dma_prepare_data(struct sdhci_host *host,
> > +                                          struct mmc_command *cmd)
> > +{
> > +     struct mmc_data *data = cmd->data;
> > +
> > +     host->data_timeout = 0;
> > +
> > +     if (sdhci_data_line_cmd(cmd))
> > +             sdhci_set_timeout(host, cmd);
> > +
> > +     WARN_ON(host->data);
> > +
> > +     /* Sanity checks */
> > +     WARN_ON(data->blksz * data->blocks > 524288);
> > +     WARN_ON(data->blksz > host->mmc->max_blk_size);
> > +     WARN_ON(data->blocks > 65535);
> > +
> > +     host->flags |= SDHCI_REQ_USE_DMA;
> > +     host->data = data;
> > +     host->data_early = 0;
> > +     host->data->bytes_xfered = 0;
> > +
> > +     sdhci_set_transfer_irqs(host);
> > +
> > +     /*
> > +      * For Version 4.10 onwards, if v4 mode is enabled, 32-bit Block Count
> > +      * can be supported, in that case 16-bit block count register must be 0.
> > +      */
> > +     if (host->version >= SDHCI_SPEC_410 && host->v4_mode &&
> > +         (host->quirks2 & SDHCI_QUIRK2_USE_32BIT_BLK_CNT)) {
> > +             if (sdhci_readw(host, SDHCI_BLOCK_COUNT))
> > +                     sdhci_writew(host, 0, SDHCI_BLOCK_COUNT);
> > +             sdhci_writew(host, data->blocks, SDHCI_32BIT_BLK_CNT);
> > +     } else {
> > +             sdhci_writew(host, data->blocks, SDHCI_BLOCK_COUNT);
> > +     }
>
> It is probably worth factoring out the code that is shared with
> sdhci_prepare_data() where possible.
>
> > +
> > +     return 0;
> > +}
> > +
> > +static void sdhci_external_dma_prepare_data(struct sdhci_host *host,
> > +                                         struct mmc_command *cmd)
> > +{
> > +     struct mmc_data *data = cmd->data;
> > +
> > +     if (!data)
> > +             return;
>
> Even in the !data case, we still need to set up a timeout for commands with
> busy waiting.  I suggest checking the !data case before calling
> sdhci_external_dma_prepare_data()

Ok.

>
> > +
> > +     if (sdhci_external_dma_setup(host, cmd) ||
> > +         __sdhci_external_dma_prepare_data(host, cmd)) {
> > +             sdhci_external_dma_release(host);
> > +             pr_err("%s: Cannot use external DMA, switch to the DMA/PIO which standard SDHCI provides.\n",
> > +                    mmc_hostname(host->mmc));
> > +             sdhci_prepare_data(host, cmd);
> > +     }
> > +}
> > +
> > +static void sdhci_external_dma_pre_transfer(struct sdhci_host *host,
> > +                                         struct mmc_command *cmd)
> > +{
> > +     struct dma_chan *chan;
> > +
> > +     if (!cmd->data || cmd->opcode == MMC_SET_BLOCK_COUNT)
>
> MMC_SET_BLOCK_COUNT never has cmd->data and so does not need to be checked.

Ok.

>
> > +             return;
> > +
> > +     sdhci_writew(host, cmd->data->blksz, SDHCI_BLOCK_SIZE);
>
> Block size is set in __sdhci_external_dma_prepare_data() so does it need to
> be set here also.

Ok.

>
> > +     chan = sdhci_external_dma_channel(host, cmd->data);
> > +     if (chan)
> > +             dma_async_issue_pending(chan);
> > +}
> > +
> > +static int sdhci_external_dma_cleanup(struct sdhci_host *host,
> > +                                 struct mmc_data *data)
>
> Please align parameters with open parenthesis
>
> > +{
> > +     struct dma_chan *chan = sdhci_external_dma_channel(host, data);
> > +     int ret = 0;
> > +
> > +     if (chan)
> > +             ret = dmaengine_terminate_async(chan);
> > +
> > +     return ret;
> > +}
> > +#else
> > +static int sdhci_external_dma_init(struct sdhci_host *host)
> > +{
> > +     return -EOPNOTSUPP;
> > +}
> > +
> > +static void sdhci_external_dma_release(struct sdhci_host *host)
> > +{}
> > +
> > +static void sdhci_external_dma_prepare_data(struct sdhci_host *host,
> > +                                         struct mmc_command *cmd)
> > +{
> > +     /* If MMC_SDHCI_EXTERNAL_DMA not supported, PIO will be used */
> > +     sdhci_prepare_data(host, cmd);
> > +}
> > +
> > +static void sdhci_external_dma_pre_transfer(struct sdhci_host *host,
> > +                                         struct mmc_command *cmd)
> > +{}
> > +
> > +static int sdhci_external_dma_cleanup(struct sdhci_host *host,
> > +                                 struct mmc_data *data)
>
> Please align parameters with open parenthesis
>
> > +{
> > +     return 0;
> > +}
> > +#endif
> > +
> > +void sdhci_switch_external_dma(struct sdhci_host *host, bool en)
> > +{
> > +     host->use_external_dma = en;
> > +}
> > +EXPORT_SYMBOL_GPL(sdhci_switch_external_dma);
> > +
> >  static inline bool sdhci_auto_cmd12(struct sdhci_host *host,
> >                                   struct mmc_request *mrq)
> >  {
> > @@ -1374,7 +1595,10 @@ void sdhci_send_command(struct sdhci_host *host, struct mmc_command *cmd)
> >               host->data_cmd = cmd;
> >       }
> >
> > -     sdhci_prepare_data(host, cmd);
> > +     if (host->use_external_dma)
>
> As mentioned above wrt sdhci_external_dma_prepare_data():
>
>         if (host->use_external_dma && cmd->data)
>

Maybe we should move checking the !data case out of both
_prepare_data, and add it to sdhci_send_command() before calling
_prepare_data(), that's saying we can do set up a timeout in
sdhci_send_command().

> > +             sdhci_external_dma_prepare_data(host, cmd);
> > +     else
> > +             sdhci_prepare_data(host, cmd);
> >
> >       sdhci_writel(host, cmd->arg, SDHCI_ARGUMENT);
> >
> > @@ -1416,6 +1640,9 @@ void sdhci_send_command(struct sdhci_host *host, struct mmc_command *cmd)
> >               timeout += 10 * HZ;
> >       sdhci_mod_timer(host, cmd->mrq, timeout);
> >
> > +     if (host->use_external_dma)
> > +             sdhci_external_dma_pre_transfer(host, cmd);
>
> Why is sdhci_external_dma_pre_transfer() needed here - couldn't it be done
> in sdhci_external_dma_prepare_data()?
>

I'm not sure dma_async_issue_pending() can be done so early in
sdhci_external_dma_prepare_data().

> > +
> >       sdhci_writew(host, SDHCI_MAKE_CMD(cmd->opcode, flags), SDHCI_COMMAND);
> >  }
> >  EXPORT_SYMBOL_GPL(sdhci_send_command);
> > @@ -1781,6 +2008,11 @@ void sdhci_request(struct mmc_host *mmc, struct mmc_request *mrq)
> >
> >       sdhci_led_activate(host);
> >
> > +     if (host->use_external_dma && mrq->data) {
> > +             struct dma_chan *chan = sdhci_external_dma_channel(host,
> > +                                                                mrq->data);
>
> sdhci_external_dma_channel is not declared if
> !IS_ENABLED(CONFIG_MMC_SDHCI_EXTERNAL_DMA)

Ok, I guess this can be moved to sdhci_external_dma_prepare_data().

>
> > +             dmaengine_synchronize(chan);
>
> So this is to cover for using dmaengine_terminate_async()?

Ok.

>
> > +     }
> >       /*
> >        * Ensure we don't send the STOP for non-SET_BLOCK_COUNTED
> >        * requests if Auto-CMD12 is enabled.
> > @@ -2658,6 +2890,8 @@ static bool sdhci_request_done(struct sdhci_host *host)
> >                               dma_unmap_sg(mmc_dev(host->mmc), data->sg,
> >                                            data->sg_len,
> >                                            mmc_get_dma_dir(data));
> > +                             if (host->use_external_dma)
> > +                                     sdhci_external_dma_cleanup(host, data);
>
> Is sdhci_external_dma_cleanup() only needed in the error case?
>
> The DMA must be stopped before the memory is unmapped and potentially freed.
>
> Isn't the DMA cleanup also needed in the bounce buffer case?
>
> Isn't the DMA cleanup also needed in the COOKIE_PRE_MAPPED case?
>
> dmaengine_terminate_async() doesn't stop the DMA but
> dmaengine_terminate_sync() is not atomic, which looks like a problem.
>
> Perhaps you look at scheduling some work for the external dma error case
> instead of calling __sdhci_finish_mrq()?  Then the work can do the
> dmaengine_terminate_sync() and call __sdhci_finish_mrq().

Ok, I will look at these issues.

>
> >                       }
> >                       data->host_cookie = COOKIE_UNMAPPED;
> >               }
> > @@ -3692,12 +3926,15 @@ int sdhci_setup_host(struct sdhci_host *host)
> >                      mmc_hostname(mmc), host->version);
> >       }
> >
> > -     if (host->quirks & SDHCI_QUIRK_FORCE_DMA)
> > +     if (host->quirks & SDHCI_QUIRK_FORCE_DMA) {
> >               host->flags |= SDHCI_USE_SDMA;
> > -     else if (!(host->caps & SDHCI_CAN_DO_SDMA))
> > +     } else if (!(host->caps & SDHCI_CAN_DO_SDMA)) {
> >               DBG("Controller doesn't have SDMA capability\n");
> > -     else
> > +     } else if (host->use_external_dma) {
> > +             /* Using dma-names to detect external dma capability */
> > +     } else {
> >               host->flags |= SDHCI_USE_SDMA;
> > +     }
>
> These if-statements are about setting SDHCI_USE_SDMA but why is a change
> needed for the host->use_external_dma case?

Yes, this is not needed, otherwise the controller cannot switch back
to SDMA if it is supported in the controller.

>
> >
> >       if ((host->quirks & SDHCI_QUIRK_BROKEN_DMA) &&
> >               (host->flags & SDHCI_USE_SDMA)) {
> > @@ -3785,6 +4022,19 @@ int sdhci_setup_host(struct sdhci_host *host)
> >               }
> >       }
> >
> > +     if (host->use_external_dma) {
> > +             ret = sdhci_external_dma_init(host);
> > +             if (ret == -EPROBE_DEFER)
> > +                     goto unreg;
> > +
> > +             /*
> > +              * Fall back to use the DMA/PIO integrated in standard SDHCI
> > +              * instead of external DMA devices.
> > +              */
> > +             if (ret)
> > +                     sdhci_switch_external_dma(host, false);
> > +     }
> > +
> >       /*
> >        * If we use DMA, then it's up to the caller to set the DMA
> >        * mask, but PIO does not need the hw shim so we set a new
> > @@ -4201,6 +4451,10 @@ void sdhci_cleanup_host(struct sdhci_host *host)
> >               dma_free_coherent(mmc_dev(mmc), host->align_buffer_sz +
> >                                 host->adma_table_sz, host->align_buffer,
> >                                 host->align_addr);
> > +
> > +     if (host->use_external_dma)
> > +             sdhci_external_dma_release(host);
> > +
> >       host->adma_table = NULL;
> >       host->align_buffer = NULL;
> >  }
> > @@ -4247,6 +4501,7 @@ int __sdhci_add_host(struct sdhci_host *host)
> >
> >       pr_info("%s: SDHCI controller on %s [%s] using %s\n",
> >               mmc_hostname(mmc), host->hw_name, dev_name(mmc_dev(mmc)),
> > +             host->use_external_dma ? "External DMA" :
> >               (host->flags & SDHCI_USE_ADMA) ?
> >               (host->flags & SDHCI_USE_64_BIT_DMA) ? "ADMA 64-bit" : "ADMA" :
> >               (host->flags & SDHCI_USE_SDMA) ? "DMA" : "PIO");
> > @@ -4335,6 +4590,9 @@ void sdhci_remove_host(struct sdhci_host *host, int dead)
> >                                 host->adma_table_sz, host->align_buffer,
> >                                 host->align_addr);
> >
> > +     if (host->use_external_dma)
> > +             sdhci_external_dma_release(host);
> > +
> >       host->adma_table = NULL;
> >       host->align_buffer = NULL;
> >  }
> > diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> > index 6cc9a3c2ac66..7a52823ebef4 100644
> > --- a/drivers/mmc/host/sdhci.h
> > +++ b/drivers/mmc/host/sdhci.h
> > @@ -482,6 +482,7 @@ struct sdhci_host {
> >
> >       int irq;                /* Device IRQ */
> >       void __iomem *ioaddr;   /* Mapped address */
> > +     phys_addr_t mapbase;    /* physical address base */
> >       char *bounce_buffer;    /* For packing SDMA reads/writes */
> >       dma_addr_t bounce_addr;
> >       unsigned int bounce_buffer_size;
> > @@ -531,6 +532,7 @@ struct sdhci_host {
> >       bool pending_reset;     /* Cmd/data reset is pending */
> >       bool irq_wake_enabled;  /* IRQ wakeup is enabled */
> >       bool v4_mode;           /* Host Version 4 Enable */
> > +     bool use_external_dma; /* Host selects to use external DMA */
>
> Please align /**/ with above i.e. use tab
>
> >
> >       struct mmc_request *mrqs_done[SDHCI_MAX_MRQS];  /* Requests done */
> >       struct mmc_command *cmd;        /* Current command */
> > @@ -559,6 +561,11 @@ struct sdhci_host {
> >       struct timer_list timer;        /* Timer for timeouts */
> >       struct timer_list data_timer;   /* Timer for data timeouts */
> >
> > +#if IS_ENABLED(CONFIG_MMC_SDHCI_EXTERNAL_DMA)
> > +     struct dma_chan *rx_chan;
> > +     struct dma_chan *tx_chan;
> > +#endif
> > +
> >       u32 caps;               /* CAPABILITY_0 */
> >       u32 caps1;              /* CAPABILITY_1 */
> >       bool read_caps;         /* Capability flags have been read */
> > @@ -792,5 +799,6 @@ void sdhci_start_tuning(struct sdhci_host *host);
> >  void sdhci_end_tuning(struct sdhci_host *host);
> >  void sdhci_reset_tuning(struct sdhci_host *host);
> >  void sdhci_send_tuning(struct sdhci_host *host, u32 opcode);
> > +void sdhci_switch_external_dma(struct sdhci_host *host, bool en);
> >
> >  #endif /* __SDHCI_HW_H */
> >
>

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