Re: [RFC PATCH 09/12] mmc: sdhci: Use software timer when timeout greater than hardware capablility

[Kishon Vijay Abraham I <kishon@ti.com>]

Hi Adrian,

On Wednesday 20 December 2017 07:41 PM, Adrian Hunter wrote:
> On 14/12/17 15:09, Kishon Vijay Abraham I wrote:
>> Errata i834 in AM572x Sitara Processors Silicon Revision 2.0, 1.1
>> (SPRZ429K July 2014–Revised March 2017 [1]) mentions
>> Under high speed HS200 and SDR104 modes, the functional clock for MMC
>> modules will reach up to 192 MHz. At this frequency, the maximum obtainable
>> timeout (DTO = 0xE) through MMC host controller is (1/192MHz)*2^27 = 700ms.
>> Commands taking longer than 700ms may be affected by this small window
>> frame. Workaround for this errata is use a software timer instead of
>> hardware timer to provide the delay requested by the upper layer.
>>
>> While this errata is specific to AM572x, it is applicable to all sdhci
>> based controllers when a particular request require timeout greater
>> than hardware capability.
> 
> It doesn't work for our controllers.  Even if the data timeout interrupt is
> disabled, it seems like the timeout still "happens" in some fashion - after
> which the host controller starts misbehaving.

even if the data timeout doesn't get disabled, count = 0xE is still present. So
ideally this shouldn't break any existing platforms no?
> 
> So you will need to add a quirk.
> 
>>
>> Re-use the software timer already implemented in sdhci to program the
>> correct timeout value and also disable the hardware timeout when
>> the required timeout is greater than hardware capabiltiy in order to
>> avoid spurious timeout interrupts.
>>
>> This patch is based on the earlier patch implemented for omap_hsmmc [2]
>>
>> [1] -> http://www.ti.com/lit/er/sprz429k/sprz429k.pdf
>> [2] -> https://patchwork.kernel.org/patch/9791449/
>>
>> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
>> ---
>>  drivers/mmc/host/sdhci.c | 41 +++++++++++++++++++++++++++++++++++++++--
>>  drivers/mmc/host/sdhci.h | 11 +++++++++++
>>  2 files changed, 50 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index e9290a3439d5..d0655e1d2cc7 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -673,6 +673,27 @@ static void sdhci_adma_table_post(struct sdhci_host *host,
>>  	}
>>  }
>>  
>> +static void sdhci_calc_sw_timeout(struct sdhci_host *host,
>> +				  struct mmc_command *cmd,
>> +				  unsigned int target_timeout)
>> +{
>> +	struct mmc_host *mmc = host->mmc;
>> +	struct mmc_ios *ios = &mmc->ios;
>> +	struct mmc_data *data = cmd->data;
>> +	unsigned long long transfer_time;
>> +
>> +	if (data) {
>> +		transfer_time = MMC_BLOCK_TRANSFER_TIME_MS(data->blksz,
>> +							   ios->bus_width,
>> +							   ios->clock);
> 
> If it has a value, actual_clock is better than ios->clock.

okay.
> 
>> +		/* calculate timeout for the entire data */
>> +		host->data_timeout = (data->blocks * (target_timeout +
>> +						      transfer_time));
>> +	} else if (cmd->flags & MMC_RSP_BUSY) {
>> +		host->data_timeout = cmd->busy_timeout * MSEC_PER_SEC;
> 
> Doesn't need MSEC_PER_SEC multiplier.

right.
> 
>> +	}
>> +}
>> +
>>  static u8 sdhci_calc_timeout(struct sdhci_host *host, struct mmc_command *cmd)
>>  {
>>  	u8 count;
>> @@ -732,8 +753,12 @@ static u8 sdhci_calc_timeout(struct sdhci_host *host, struct mmc_command *cmd)
>>  	}
>>  
>>  	if (count >= 0xF) {
>> -		DBG("Too large timeout 0x%x requested for CMD%d!\n",
>> -		    count, cmd->opcode);
>> +		DBG("Too large timeout.. using SW timeout for CMD%d!\n",
>> +		    cmd->opcode);
>> +		sdhci_calc_sw_timeout(host, cmd, target_timeout);
>> +		host->ier &= ~SDHCI_INT_DATA_TIMEOUT;
>> +		sdhci_writel(host, host->ier, SDHCI_INT_ENABLE);
>> +		sdhci_writel(host, host->ier, SDHCI_SIGNAL_ENABLE);
>>  		count = 0xE;
>>  	}
>>  
>> @@ -1198,6 +1223,14 @@ static void sdhci_finish_command(struct sdhci_host *host)
>>  {
>>  	struct mmc_command *cmd = host->cmd;
>>  
>> +	if (host->data_timeout) {
>> +		unsigned long timeout;
>> +
>> +		timeout = jiffies +
>> +			  msecs_to_jiffies(host->data_timeout);
>> +		sdhci_mod_timer(host, host->cmd->mrq, timeout);
> 
> cmd could be the sbc or a stop cmd or a command during transfer, so this
> needs more logic.

host->data_timeout gets set only for data commands or commands with busy
timeout. But I guess for commands during data transfer, host->data_timeout
might still be set?

Checking sdhci_data_line_cmd(mrq->cmd) in addition to host->data_timeout should
take care of all cases right?
> 
>> +	}
>> +
>>  	host->cmd = NULL;
>>  
>>  	if (cmd->flags & MMC_RSP_PRESENT) {
>> @@ -2341,6 +2374,10 @@ static bool sdhci_request_done(struct sdhci_host *host)
>>  		return true;
>>  	}
>>  
>> +	host->data_timeout = 0;
>> +	host->ier |= SDHCI_INT_DATA_TIMEOUT;
>> +	sdhci_writel(host, host->ier, SDHCI_INT_ENABLE);
>> +	sdhci_writel(host, host->ier, SDHCI_SIGNAL_ENABLE);
> 
> sdhci can have 2 requests in progress to allow for commands to be sent while
> a data transfer is in progress, so this is not necessarily the data transfer
> request that is done.  Also we want to avoid unnecessary register writes.
> 

okay.. got it.
>>  	sdhci_del_timer(host, mrq);
>>  
>>  	/*
>> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
>> index 54bc444c317f..e6e0278bea1a 100644
>> --- a/drivers/mmc/host/sdhci.h
>> +++ b/drivers/mmc/host/sdhci.h
>> @@ -332,6 +332,15 @@ struct sdhci_adma2_64_desc {
>>  /* Allow for a a command request and a data request at the same time */
>>  #define SDHCI_MAX_MRQS		2
>>  
>> +/*
>> + * Time taken for transferring one block. It is multiplied by a constant
>> + * factor '2' to account for any errors
>> + */
>> +#define MMC_BLOCK_TRANSFER_TIME_MS(blksz, bus_width, freq)		\
>> +				   ((unsigned long long)		\
>> +				   (2 * (((blksz) * MSEC_PER_SEC *	\
>> +				   (8 / (bus_width))) / (freq))))
> 
> I don't think the macro helps make the code more readable.  Might just as
> well write a nice function to calculate the entire data request timeout.

okay.
> 
>> +
>>  enum sdhci_cookie {
>>  	COOKIE_UNMAPPED,
>>  	COOKIE_PRE_MAPPED,	/* mapped by sdhci_pre_req() */
>> @@ -546,6 +555,8 @@ struct sdhci_host {
>>  	/* Host SDMA buffer boundary. */
>>  	u32			sdma_boundary;
>>  
>> +	unsigned long long	data_timeout;
> 
> msecs_to_jiffies() will truncate to 'unsigned int' anyway, so this might as
> well be 'unsigned int'.
> 

okay.

Thanks
Kishon