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

Faiz Abbas
2019-02-11T12:23:57Z

Hi Adrian,

On 24/01/19 5:10 PM, Adrian Hunter 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.
>[snip]>> /*
>> * 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().
>

Why don't we get rid of the finish_tasklet and use the already existing
threaded_irq for everything? I tested the following patch out and it
seems to work well. This enables us to just call
dmaengine_terminate_sync() in sdhci_request_done().

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index a22e11a65658..beff2ac2dee5 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1232,7 +1232,7 @@ static void __sdhci_finish_mrq(struct sdhci_host
*host, struct mmc_request *mrq)

WARN_ON(i >= SDHCI_MAX_MRQS);

- tasklet_schedule(&host->finish_tasklet);
+ host->threaded_irq_needed = true;
}

static void sdhci_finish_mrq(struct sdhci_host *host, struct
mmc_request *mrq)
@@ -2705,14 +2705,6 @@ static bool sdhci_request_done(struct sdhci_host
*host)
return false;
}

-static void sdhci_tasklet_finish(unsigned long param)
-{
- struct sdhci_host *host = (struct sdhci_host *)param;
-
- while (!sdhci_request_done(host))
- ;
-}
-
static void sdhci_timeout_timer(struct timer_list *t)
{
struct sdhci_host *host;
@@ -3000,6 +2992,8 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
u32 intmask, mask, unexpected = 0;
int max_loops = 16;

+ host->threaded_irq_needed = false;
+
spin_lock(&host->lock);

if (host->runtime_suspended && !sdhci_sdio_irq_enabled(host)) {
@@ -3077,6 +3071,9 @@ static irqreturn_t sdhci_irq(int irq, void *dev_id)
result = IRQ_WAKE_THREAD;
}

+ if (host->threaded_irq_needed)
+ result = IRQ_WAKE_THREAD;
+
intmask &= ~(SDHCI_INT_CARD_INSERT | SDHCI_INT_CARD_REMOVE |
SDHCI_INT_CMD_MASK | SDHCI_INT_DATA_MASK |
SDHCI_INT_ERROR | SDHCI_INT_BUS_POWER |
@@ -3131,6 +3128,10 @@ static irqreturn_t sdhci_thread_irq(int irq, void
*dev_id)
spin_unlock_irqrestore(&host->lock, flags);
}

+ do {
+ isr = sdhci_request_done(host);
+ } while(isr);
+
return isr ? IRQ_HANDLED : IRQ_NONE;
}

@@ -4211,12 +4212,6 @@ int __sdhci_add_host(struct sdhci_host *host)
struct mmc_host *mmc = host->mmc;
int ret;

- /*
- * Init tasklets.
- */
- tasklet_init(&host->finish_tasklet,
- sdhci_tasklet_finish, (unsigned long)host);
-
timer_setup(&host->timer, sdhci_timeout_timer, 0);
timer_setup(&host->data_timer, sdhci_timeout_data_timer, 0);

@@ -4229,7 +4224,7 @@ int __sdhci_add_host(struct sdhci_host *host)
if (ret) {
pr_err("%s: Failed to request IRQ %d: %d\n",
mmc_hostname(mmc), host->irq, ret);
- goto untasklet;
+ return ret;
}

ret = sdhci_led_register(host);
@@ -4262,8 +4257,6 @@ int __sdhci_add_host(struct sdhci_host *host)
sdhci_writel(host, 0, SDHCI_INT_ENABLE);
sdhci_writel(host, 0, SDHCI_SIGNAL_ENABLE);
free_irq(host->irq, host);
-untasklet:
- tasklet_kill(&host->finish_tasklet);

return ret;
}
@@ -4325,8 +4318,6 @@ void sdhci_remove_host(struct sdhci_host *host,
int dead)
del_timer_sync(&host->timer);
del_timer_sync(&host->data_timer);

- tasklet_kill(&host->finish_tasklet);
-
if (!IS_ERR(mmc->supply.vqmmc))
regulator_disable(mmc->supply.vqmmc);

diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
index 6cc9a3c2ac66..abf4f77650b5 100644
--- a/drivers/mmc/host/sdhci.h
+++ b/drivers/mmc/host/sdhci.h
@@ -554,7 +554,7 @@ struct sdhci_host {

unsigned int desc_sz; /* ADMA descriptor size */

- struct tasklet_struct finish_tasklet; /* Tasklet structures */
+ bool threaded_irq_needed;

struct timer_list timer; /* Timer for timeouts */
struct timer_list data_timer; /* Timer for data timeouts */

Thanks,
Faiz