Re: [PATCH 1/7] mmc: sdhci: add support for using external DMA devices

Chunyan Zhang
2019-01-28T10:20:28Z

On Thu, 24 Jan 2019 at 19:41, Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> On 11/01/19 1:08 PM, Faiz Abbas 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
> > 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@linaro.org>
> > Signed-off-by: Faiz Abbas <faiz_abbas@ti.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 */
> >
>