Re: [RFC PATCH v3.1 21/27] mmc: sdhci-uhs2: add irq() and others

Adrian Hunter
2020-12-08T08:38:13Z

On 8/12/20 9:37 am, AKASHI Takahiro wrote:
> On Tue, Dec 01, 2020 at 06:46:39PM +0200, Adrian Hunter wrote:
>> On 6/11/20 4:27 am, AKASHI Takahiro wrote:
>>> This is a UHS-II version of sdhci's request() operation.
>>> It handles UHS-II related command interrupts and errors.
>>>
>>> Signed-off-by: Ben Chuang <ben.chuang@genesyslogic.com.tw>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
>>> ---
>>> drivers/mmc/host/sdhci-uhs2.c | 247 ++++++++++++++++++++++++++++++++++
>>> drivers/mmc/host/sdhci-uhs2.h | 3 +
>>> drivers/mmc/host/sdhci.c | 112 ++++++++-------
>>> drivers/mmc/host/sdhci.h | 6 +
>>> 4 files changed, 319 insertions(+), 49 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/sdhci-uhs2.c b/drivers/mmc/host/sdhci-uhs2.c
>>> index 36e52553977a..d50134e912f3 100644
>>> --- a/drivers/mmc/host/sdhci-uhs2.c
>>> +++ b/drivers/mmc/host/sdhci-uhs2.c
>>> @@ -11,6 +11,7 @@
>>> */
>>>
>>> #include <linux/delay.h>
>>> +#include <linux/dmaengine.h>
>>> #include <linux/ktime.h>
>>> #include <linux/module.h>
>>> #include <linux/mmc/mmc.h>
>>> @@ -670,6 +671,12 @@ static inline void sdhci_external_dma_pre_transfer(struct sdhci_host *host,
>>> struct mmc_command *cmd)
>>> {
>>> }
>>> +
>>> +static inline struct dma_chan *sdhci_external_dma_channel(struct sdhci_host *host,
>>> + struct mmc_data *data)
>>> +{
>>> + return NULL;
>>> +}
>>> #endif /* CONFIG_MMC_SDHCI_EXTERNAL_DMA */
>>>
>>> static void sdhci_uhs2_finish_data(struct sdhci_host *host)
>>> @@ -1051,6 +1058,246 @@ static void sdhci_uhs2_finish_command(struct sdhci_host *host)
>>> }
>>> }
>>>
>>> +/*****************************************************************************\
>>> + * *
>>> + * Request done *
>>> + * *
>>> +\*****************************************************************************/
>>> +
>>> +static bool sdhci_uhs2_request_done(struct sdhci_host *host)
>>> +{
>>> + unsigned long flags;
>>> + struct mmc_request *mrq;
>>> + int i;
>>> +
>>> + /* FIXME: UHS2_INITIALIZED, instead? */
>>> + if (!(host->mmc->flags & MMC_UHS2_SUPPORT))
>>> + return sdhci_request_done(host);
>>> +
>>> + spin_lock_irqsave(&host->lock, flags);
>>> +
>>> + for (i = 0; i < SDHCI_MAX_MRQS; i++) {
>>> + mrq = host->mrqs_done[i];
>>> + if (mrq)
>>> + break;
>>> + }
>>> +
>>> + if (!mrq) {
>>> + spin_unlock_irqrestore(&host->lock, flags);
>>> + return true;
>>> + }
>>> +
>>> + /*
>>> + * Always unmap the data buffers if they were mapped by
>>> + * sdhci_prepare_data() whenever we finish with a request.
>>> + * This avoids leaking DMA mappings on error.
>>> + */
>>> + if (host->flags & SDHCI_REQ_USE_DMA) {
>>> + struct mmc_data *data = mrq->data;
>>> +
>>> + if (host->use_external_dma && data &&
>>> + (mrq->cmd->error || data->error)) {
>>> + struct dma_chan *chan = sdhci_external_dma_channel(host, data);
>>> +
>>> + host->mrqs_done[i] = NULL;
>>> + spin_unlock_irqrestore(&host->lock, flags);
>>> + dmaengine_terminate_sync(chan);
>>> + spin_lock_irqsave(&host->lock, flags);
>>> + sdhci_set_mrq_done(host, mrq);
>>> + }
>>> +
>>> + sdhci_request_done_dma(host, mrq);
>>> + }
>>> +
>>> + /*
>>> + * The controller needs a reset of internal state machines
>>> + * upon error conditions.
>>> + */
>>> + if (sdhci_needs_reset(host, mrq)) {
>>> + /*
>>> + * Do not finish until command and data lines are available for
>>> + * reset. Note there can only be one other mrq, so it cannot
>>> + * also be in mrqs_done, otherwise host->cmd and host->data_cmd
>>> + * would both be null.
>>> + */
>>> + if (host->cmd || host->data_cmd) {
>>> + spin_unlock_irqrestore(&host->lock, flags);
>>> + return true;
>>> + }
>>> +
>>> + /* Some controllers need this kick or reset won't work here */
>>> + if (host->quirks & SDHCI_QUIRK_CLOCK_BEFORE_RESET)
>>> + /* This is to force an update */
>>> + host->ops->set_clock(host, host->clock);
>>> +
>>> + sdhci_uhs2_reset(host, SDHCI_UHS2_SW_RESET_SD);
>>
>> It should be possible to use the ->reset() callback for UHS-II also, then
>> this function wouldn't be needed.
>
> The reason that I didn't so is that the second argument is 'u8' for
> legacy, and u16 for uhs-2, more importantly that the register to be
> accessed here is different and hence that the same bit may have a different
> meaning/semantics. I thought that this kind of dependency can be confusing
> and should be avoided.

We can always add comments to explain it.

Currently, there are 4 possibilities for reset:
1. full reset i.e. SDHCI_RESET_ALL : all standard registers are reset to
default values
2. reset command circuit i.e. SDHCI_RESET_CMD : error recovery for commands
3. reset data circuit i.e. SDHCI_RESET_DATA : error recovery for data
4. 2 + 3

My brief reading of the spec (might be wrong) suggests mapping:

SD mode UHS-II mode
SDHCI_RESET_ALL SDHCI_UHS2_SW_RESET_FULL
SDHCI_RESET_CMD SDHCI_RESET_CMD
SDHCI_RESET_DATA SDHCI_UHS2_SW_RESET_SD

>
> That said, if you really want to use reset hook, I'd defer to you.
>
>>
>>> + host->pending_reset = false;
>>> + }
>>> +
>>> + host->mrqs_done[i] = NULL;
>>> +
>>> + spin_unlock_irqrestore(&host->lock, flags);
>>> +
>>> + if (host->ops->request_done)
>>> + host->ops->request_done(host, mrq);
>>> + else
>>> + mmc_request_done(host->mmc, mrq);
>>> +
>>> + return false;
>>> +}
>>> +
>>> +static void sdhci_uhs2_complete_work(struct work_struct *work)
>>> +{
>>> + struct sdhci_host *host = container_of(work, struct sdhci_host,
>>> + complete_work);
>>> +
>>> + while (!sdhci_uhs2_request_done(host))
>>> + ;
>>> +}
>>> +
>>> +/*****************************************************************************\
>>> + * *
>>> + * Interrupt handling *
>>> + * *
>>> +\*****************************************************************************/
>>> +
>>> +static void __sdhci_uhs2_irq(struct sdhci_host *host, u32 uhs2mask)
>>> +{
>>> + struct mmc_command *cmd = host->cmd;
>>> +
>>> + DBG("*** %s got UHS2 error interrupt: 0x%08x\n",
>>> + mmc_hostname(host->mmc), uhs2mask);
>>> +
>>> + if (uhs2mask & SDHCI_UHS2_ERR_INT_STATUS_CMD_MASK) {
>>> + if (!host->cmd) {
>>> + pr_err("%s: Got cmd interrupt 0x%08x but no cmd.\n",
>>> + mmc_hostname(host->mmc),
>>> + (unsigned int)uhs2mask);
>>> + sdhci_dumpregs(host);
>>> + return;
>>> + }
>>> + host->cmd->error = -EILSEQ;
>>> + if (uhs2mask & SDHCI_UHS2_ERR_INT_STATUS_RES_TIMEOUT)
>>> + host->cmd->error = -ETIMEDOUT;
>>> + }
>>> +
>>> + if (uhs2mask & SDHCI_UHS2_ERR_INT_STATUS_DATA_MASK) {
>>> + if (!host->data) {
>>> + pr_err("%s: Got data interrupt 0x%08x but no data.\n",
>>> + mmc_hostname(host->mmc),
>>> + (unsigned int)uhs2mask);
>>> + sdhci_dumpregs(host);
>>> + return;
>>> + }
>>> +
>>> + if (uhs2mask & SDHCI_UHS2_ERR_INT_STATUS_DEADLOCK_TIMEOUT) {
>>> + pr_err("%s: Got deadlock timeout interrupt 0x%08x\n",
>>> + mmc_hostname(host->mmc),
>>> + (unsigned int)uhs2mask);
>>> + host->data->error = -ETIMEDOUT;
>>> + } else if (uhs2mask & SDHCI_UHS2_ERR_INT_STATUS_ADMA) {
>>> + pr_err("%s: ADMA error = 0x %x\n",
>>> + mmc_hostname(host->mmc),
>>> + sdhci_readb(host, SDHCI_ADMA_ERROR));
>>> + host->data->error = -EIO;
>>> + } else {
>>> + host->data->error = -EILSEQ;
>>> + }
>>> + }
>>> +
>>> + if (host->data && host->data->error)
>>> + sdhci_uhs2_finish_data(host);
>>> + else
>>> + sdhci_finish_mrq(host, cmd->mrq);
>>> +}
>>> +
>>> +u32 sdhci_uhs2_irq(struct sdhci_host *host, u32 intmask)
>>> +{
>>> + u32 mask = intmask, uhs2mask;
>>> +
>>> + if (!(host->mmc->flags & MMC_UHS2_SUPPORT))
>>> + goto out;
>>> +
>>> + /*
>>> + * TODO: We should mask Normal Error Interrupt Status Register
>>> + * in UHS-2 mode so that we don't have to care SD mode errors.
>>> + */
>>> + if (intmask & SDHCI_INT_ERROR) {
>>> + uhs2mask = sdhci_readl(host, SDHCI_UHS2_ERR_INT_STATUS);
>>> + if (!(uhs2mask & SDHCI_UHS2_ERR_INT_STATUS_MASK))
>>> + goto cmd_irq;
>>> +
>>> + /* Clear error interrupts */
>>> + sdhci_writel(host, uhs2mask & SDHCI_UHS2_ERR_INT_STATUS_MASK,
>>> + SDHCI_UHS2_ERR_INT_STATUS);
>>> +
>>> + /* Handle error interrupts */
>>> + __sdhci_uhs2_irq(host, uhs2mask);
>>> +
>>> + /* Caller, shdci_irq(), doesn't have to care UHS-2 errors */
>>> + intmask &= ~SDHCI_INT_ERROR;
>>> + mask &= SDHCI_INT_ERROR;
>>> + }
>>> +
>>> +cmd_irq:
>>> + /*
>>> + * TODO: Cleanup
>>> + * INT_RESPONSE is enough instead of INT_CMD_MASK, assuming that
>>> + * INT_ERROR and INT_CMD_MASK won't happen at the same time.
>>> + */
>>> + if (intmask & SDHCI_INT_CMD_MASK) {
>>> + /* Clear command interrupt */
>>> + sdhci_writel(host, intmask & SDHCI_INT_CMD_MASK,
>>> + SDHCI_INT_STATUS);
>>> +
>>> + /* Handle command interrupt */
>>> + if (intmask & SDHCI_INT_RESPONSE)
>>> + sdhci_uhs2_finish_command(host);
>>> +
>>> + /* Caller, shdci_irq(), doesn't have to care UHS-2 command */
>>> + intmask &= ~SDHCI_INT_CMD_MASK;
>>> + mask &= SDHCI_INT_CMD_MASK;
>>> + }
>>> +
>>> + /* Clear already-handled interrupts. */
>>> + sdhci_writel(host, mask, SDHCI_INT_STATUS);
>>> +
>>> +out:
>>> + return intmask;
>>> +}
>>> +EXPORT_SYMBOL_GPL(sdhci_uhs2_irq);
>>> +
>>> +static irqreturn_t sdhci_uhs2_thread_irq(int irq, void *dev_id)
>>> +{
>>> + struct sdhci_host *host = dev_id;
>>> + struct mmc_command *cmd;
>>> + unsigned long flags;
>>> + u32 isr;
>>> +
>>> + while (!sdhci_uhs2_request_done(host))
>>> + ;
>>> +
>>> + spin_lock_irqsave(&host->lock, flags);
>>> +
>>> + isr = host->thread_isr;
>>> + host->thread_isr = 0;
>>> +
>>> + cmd = host->deferred_cmd;
>>
>> We don't need to use deferred_cmd, so then this function should not be
>> needed.
>
> I think that you meant that we should stick to sdhci_thread_irq() here.
> Right?
>
> -Takahiro Akashi
>
>> For UHS-II we should require that the upper layer sends the abort
>> command, so all the driver needs to do to handle errors, is to reset - which
>> is already handled by sdhci_request_done() if you make use of the ->reset()
>> callback.
>>
>>> + if (cmd && !sdhci_uhs2_send_command_retry(host, cmd, flags))
>>> + sdhci_finish_mrq(host, cmd->mrq);
>>> +
>>> + spin_unlock_irqrestore(&host->lock, flags);
>>> +
>>> + if (isr & (SDHCI_INT_CARD_INSERT | SDHCI_INT_CARD_REMOVE)) {
>>> + struct mmc_host *mmc = host->mmc;
>>> +
>>> + mmc->ops->card_event(mmc);
>>> + mmc_detect_change(mmc, msecs_to_jiffies(200));
>>> + }
>>> +
>>> + return IRQ_HANDLED;
>>> +}
>>> +
>>> /*****************************************************************************\
>>> * *
>>> * Driver init/exit *
>>> diff --git a/drivers/mmc/host/sdhci-uhs2.h b/drivers/mmc/host/sdhci-uhs2.h
>>> index c1ff4ac1ab7a..b74af641d00e 100644
>>> --- a/drivers/mmc/host/sdhci-uhs2.h
>>> +++ b/drivers/mmc/host/sdhci-uhs2.h
>>> @@ -215,5 +215,8 @@ void sdhci_uhs2_set_power(struct sdhci_host *host, unsigned char mode,
>>> unsigned short vdd);
>>> void sdhci_uhs2_set_timeout(struct sdhci_host *host, struct mmc_command *cmd);
>>> void sdhci_uhs2_clear_set_irqs(struct sdhci_host *host, u32 clear, u32 set);
>>> +void sdhci_uhs2_request(struct mmc_host *mmc, struct mmc_request *mrq);
>>> +int sdhci_uhs2_request_atomic(struct mmc_host *mmc, struct mmc_request *mrq);
>>> +u32 sdhci_uhs2_irq(struct sdhci_host *host, u32 intmask);
>>>
>>> #endif /* __SDHCI_UHS2_H */
>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>> index a9f5449bddcc..e2dfc7767bcf 100644
>>> --- a/drivers/mmc/host/sdhci.c
>>> +++ b/drivers/mmc/host/sdhci.c
>>> @@ -1215,11 +1215,12 @@ static int sdhci_external_dma_init(struct sdhci_host *host)
>>> return ret;
>>> }
>>>
>>> -static struct dma_chan *sdhci_external_dma_channel(struct sdhci_host *host,
>>> - struct mmc_data *data)
>>> +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;
>>> }
>>> +EXPORT_SYMBOL_GPL(sdhci_external_dma_channel);
>>>
>>> int sdhci_external_dma_setup(struct sdhci_host *host, struct mmc_command *cmd)
>>> {
>>> @@ -1466,7 +1467,7 @@ static void sdhci_set_transfer_mode(struct sdhci_host *host,
>>> sdhci_writew(host, mode, SDHCI_TRANSFER_MODE);
>>> }
>>>
>>> -static bool sdhci_needs_reset(struct sdhci_host *host, struct mmc_request *mrq)
>>> +bool sdhci_needs_reset(struct sdhci_host *host, struct mmc_request *mrq)
>>> {
>>> return (!(host->flags & SDHCI_DEVICE_DEAD) &&
>>> ((mrq->cmd && mrq->cmd->error) ||
>>> @@ -1474,8 +1475,9 @@ static bool sdhci_needs_reset(struct sdhci_host *host, struct mmc_request *mrq)
>>> (mrq->data && mrq->data->stop && mrq->data->stop->error) ||
>>> (host->quirks & SDHCI_QUIRK_RESET_AFTER_REQUEST)));
>>> }
>>> +EXPORT_SYMBOL_GPL(sdhci_needs_reset);
>>>
>>> -static void sdhci_set_mrq_done(struct sdhci_host *host, struct mmc_request *mrq)
>>> +void sdhci_set_mrq_done(struct sdhci_host *host, struct mmc_request *mrq)
>>> {
>>> int i;
>>>
>>> @@ -1495,6 +1497,7 @@ static void sdhci_set_mrq_done(struct sdhci_host *host, struct mmc_request *mrq)
>>>
>>> WARN_ON(i >= SDHCI_MAX_MRQS);
>>> }
>>> +EXPORT_SYMBOL_GPL(sdhci_set_mrq_done);
>>>
>>> void __sdhci_finish_mrq(struct sdhci_host *host, struct mmc_request *mrq)
>>> {
>>> @@ -3029,7 +3032,56 @@ static const struct mmc_host_ops sdhci_ops = {
>>> * *
>>> \*****************************************************************************/
>>>
>>> -static bool sdhci_request_done(struct sdhci_host *host)
>>> +void sdhci_request_done_dma(struct sdhci_host *host, struct mmc_request *mrq)
>>> +{
>>> + struct mmc_data *data = mrq->data;
>>> +
>>> + if (data && data->host_cookie == COOKIE_MAPPED) {
>>> + if (host->bounce_buffer) {
>>> + /*
>>> + * On reads, copy the bounced data into the
>>> + * sglist
>>> + */
>>> + if (mmc_get_dma_dir(data) == DMA_FROM_DEVICE) {
>>> + unsigned int length = data->bytes_xfered;
>>> +
>>> + if (length > host->bounce_buffer_size) {
>>> + pr_err("%s: bounce buffer is %u bytes but DMA claims to have transferred %u bytes\n",
>>> + mmc_hostname(host->mmc),
>>> + host->bounce_buffer_size,
>>> + data->bytes_xfered);
>>> + /* Cap it down and continue */
>>> + length = host->bounce_buffer_size;
>>> + }
>>> + dma_sync_single_for_cpu(
>>> + host->mmc->parent,
>>> + host->bounce_addr,
>>> + host->bounce_buffer_size,
>>> + DMA_FROM_DEVICE);
>>> + sg_copy_from_buffer(data->sg,
>>> + data->sg_len,
>>> + host->bounce_buffer,
>>> + length);
>>> + } else {
>>> + /* No copying, just switch ownership */
>>> + dma_sync_single_for_cpu(
>>> + host->mmc->parent,
>>> + host->bounce_addr,
>>> + host->bounce_buffer_size,
>>> + mmc_get_dma_dir(data));
>>> + }
>>> + } else {
>>> + /* Unmap the raw data */
>>> + dma_unmap_sg(mmc_dev(host->mmc), data->sg,
>>> + data->sg_len,
>>> + mmc_get_dma_dir(data));
>>> + }
>>> + data->host_cookie = COOKIE_UNMAPPED;
>>> + }
>>> +}
>>> +EXPORT_SYMBOL_GPL(sdhci_request_done_dma);
>>> +
>>> +bool sdhci_request_done(struct sdhci_host *host)
>>> {
>>> unsigned long flags;
>>> struct mmc_request *mrq;
>>> @@ -3067,48 +3119,7 @@ static bool sdhci_request_done(struct sdhci_host *host)
>>> sdhci_set_mrq_done(host, mrq);
>>> }
>>>
>>> - if (data && data->host_cookie == COOKIE_MAPPED) {
>>> - if (host->bounce_buffer) {
>>> - /*
>>> - * On reads, copy the bounced data into the
>>> - * sglist
>>> - */
>>> - if (mmc_get_dma_dir(data) == DMA_FROM_DEVICE) {
>>> - unsigned int length = data->bytes_xfered;
>>> -
>>> - if (length > host->bounce_buffer_size) {
>>> - pr_err("%s: bounce buffer is %u bytes but DMA claims to have transferred %u bytes\n",
>>> - mmc_hostname(host->mmc),
>>> - host->bounce_buffer_size,
>>> - data->bytes_xfered);
>>> - /* Cap it down and continue */
>>> - length = host->bounce_buffer_size;
>>> - }
>>> - dma_sync_single_for_cpu(
>>> - host->mmc->parent,
>>> - host->bounce_addr,
>>> - host->bounce_buffer_size,
>>> - DMA_FROM_DEVICE);
>>> - sg_copy_from_buffer(data->sg,
>>> - data->sg_len,
>>> - host->bounce_buffer,
>>> - length);
>>> - } else {
>>> - /* No copying, just switch ownership */
>>> - dma_sync_single_for_cpu(
>>> - host->mmc->parent,
>>> - host->bounce_addr,
>>> - host->bounce_buffer_size,
>>> - mmc_get_dma_dir(data));
>>> - }
>>> - } else {
>>> - /* Unmap the raw data */
>>> - dma_unmap_sg(mmc_dev(host->mmc), data->sg,
>>> - data->sg_len,
>>> - mmc_get_dma_dir(data));
>>> - }
>>> - data->host_cookie = COOKIE_UNMAPPED;
>>> - }
>>> + sdhci_request_done_dma(host, mrq);
>>> }
>>>
>>> /*
>>> @@ -3132,8 +3143,10 @@ static bool sdhci_request_done(struct sdhci_host *host)
>>> /* This is to force an update */
>>> host->ops->set_clock(host, host->clock);
>>>
>>> - /* Spec says we should do both at the same time, but Ricoh
>>> - controllers do not like that. */
>>> + /*
>>> + * Spec says we should do both at the same time, but
>>> + * Ricoh controllers do not like that.
>>> + */
>>> sdhci_do_reset(host, SDHCI_RESET_CMD);
>>> sdhci_do_reset(host, SDHCI_RESET_DATA);
>>>
>>> @@ -3151,6 +3164,7 @@ static bool sdhci_request_done(struct sdhci_host *host)
>>>
>>> return false;
>>> }
>>> +EXPORT_SYMBOL_GPL(sdhci_request_done);
>>>
>>> static void sdhci_complete_work(struct work_struct *work)
>>> {
>>> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
>>> index 6eeb74741da3..74572b54ec47 100644
>>> --- a/drivers/mmc/host/sdhci.h
>>> +++ b/drivers/mmc/host/sdhci.h
>>> @@ -845,8 +845,12 @@ void __sdhci_external_dma_prepare_data(struct sdhci_host *host,
>>> struct mmc_command *cmd);
>>> void sdhci_external_dma_pre_transfer(struct sdhci_host *host,
>>> struct mmc_command *cmd);
>>> +struct dma_chan *sdhci_external_dma_channel(struct sdhci_host *host,
>>> + struct mmc_data *data);
>>> #endif
>>> bool sdhci_manual_cmd23(struct sdhci_host *host, struct mmc_request *mrq);
>>> +bool sdhci_needs_reset(struct sdhci_host *host, struct mmc_request *mrq);
>>> +void sdhci_set_mrq_done(struct sdhci_host *host, struct mmc_request *mrq);
>>> void __sdhci_finish_mrq(struct sdhci_host *host, struct mmc_request *mrq);
>>> void sdhci_finish_mrq(struct sdhci_host *host, struct mmc_request *mrq);
>>> void __sdhci_finish_data_common(struct sdhci_host *host);
>>> @@ -878,6 +882,8 @@ void sdhci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios);
>>> int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
>>> struct mmc_ios *ios);
>>> void sdhci_enable_sdio_irq(struct mmc_host *mmc, int enable);
>>> +void sdhci_request_done_dma(struct sdhci_host *host, struct mmc_request *mrq);
>>> +bool sdhci_request_done(struct sdhci_host *host);
>>> void sdhci_adma_write_desc(struct sdhci_host *host, void **desc,
>>> dma_addr_t addr, int len, unsigned int cmd);
>>>
>>>
>>