Re: [PATCH 1/3] mci: add DSR support

[Markus Niebel <list-09_barebox@tqsc.de>]

Hello Sascha,
Am 10.01.2014 12:18, wrote Sascha Hauer:
> Hi Markus,
> 
> On Fri, Jan 10, 2014 at 10:29:49AM +0100, Markus Niebel wrote:
>> From: Markus Niebel <Markus.Niebel@tqs.de>
>>
>> The eMMC and the SD-Card specifications describe the optional SET_DSR command.
>> During measurements at our lab we found that some cards implementing this feature
>> having really strong driver strengts per default. This can lead to voltage peaks
>> above the specification of the host on signal edges for data sent from a card to
>> the host.
>>
>> Since availability of a given card type may be shorter than the time a certain
>> hardware will be produced it is useful to have support for this command (Alternative
>> would be changing termination resistors and adapting the driver strength of the
>> host to the used card.)
> 
> So not all cards support this command. Have you tested it with cards
> that do not support it to make sure they still work? With eMMC you know
> at board level whether or not this command is supported, but with SD
> cards you don't.
> 

No tests done with SD-cards (SD card spec states, that DSR can be implemented, 
but we found no card, that implements this feature).

On the eMMC side we did tests with TQMa53 (barebox and u-boot) and TQMa6 
(u-boot only) and also with i.MX28 based platform:

if a card does not support DSR - CMD4 is never sent
if a card supports DSR but board does not activate the feature - CMD4 is never sent
if a card supports DSR and board code requests the feature - CMD4 is sent with the
configured value.

Would it be a good idea to document the feature as intended for non removable cards
where the exact value is known?

> Sascha
> 
Markus
>>
>> Signed-off-by: Markus Niebel <Markus.Niebel@tqs.de>
>> ---
>>  drivers/mci/mci-core.c |   27 +++++++++++++++++++++++++++
>>  include/mci.h          |    3 +++
>>  2 files changed, 30 insertions(+)
>>
>> diff --git a/drivers/mci/mci-core.c b/drivers/mci/mci-core.c
>> index a232679..2c91ff2 100644
>> --- a/drivers/mci/mci-core.c
>> +++ b/drivers/mci/mci-core.c
>> @@ -102,6 +102,20 @@ static void mci_setup_cmd(struct mci_cmd *p, unsigned cmd, unsigned arg, unsigne
>>  }
>>  
>>  /**
>> + * configure optional DSR value
>> + * @param mci_dev MCI instance
>> + * @return Transaction status (0 on success)
>> + */
>> +static int mci_set_dsr(struct mci *mci)
>> +{
>> +	struct mci_cmd cmd;
>> +
>> +	mci_setup_cmd(&cmd, MMC_CMD_SET_DSR,
>> +			(mci->host->dsr_val >> 16) | 0xffff, MMC_RSP_NONE);
>> +	return mci_send_cmd(mci, &cmd, NULL);
>> +}
>> +
>> +/**
>>   * Setup SD/MMC card's blocklength to be used for future transmitts
>>   * @param mci_dev MCI instance
>>   * @param len Blocklength in bytes
>> @@ -836,6 +850,15 @@ static void mci_extract_card_capacity_from_csd(struct mci *mci)
>>  	dev_dbg(&mci->dev, "Capacity: %u MiB\n", (unsigned)(mci->capacity >> 20));
>>  }
>>  
>> +/**
>> + * Extract card's DSR implementation state from CSD
>> + * @param mci MCI instance
>> + */
>> +static void mci_extract_card_dsr_imp_from_csd(struct mci *mci)
>> +{
>> +	mci->dsr_imp = UNSTUFF_BITS(mci->csd, 76, 1);
>> +}
>> +
>>  static int mmc_compare_ext_csds(struct mci *mci, unsigned bus_width)
>>  {
>>  	u8 *bw_ext_csd;
>> @@ -1058,6 +1081,7 @@ static int mci_startup(struct mci *mci)
>>  	mci_detect_version_from_csd(mci);
>>  	mci_extract_max_tran_speed_from_csd(mci);
>>  	mci_extract_block_lengths_from_csd(mci);
>> +	mci_extract_card_dsr_imp_from_csd(mci);
>>  
>>  	/* sanitiy? */
>>  	if (mci->read_bl_len > SECTOR_SIZE) {
>> @@ -1074,6 +1098,9 @@ static int mci_startup(struct mci *mci)
>>  	dev_dbg(&mci->dev, "Read block length: %u, Write block length: %u\n",
>>  		mci->read_bl_len, mci->write_bl_len);
>>  
>> +	if (mci->dsr_imp && mci->host->use_dsr)
>> +		mci_set_dsr(mci);
>> +
>>  	if (!mmc_host_is_spi(host)) { /* cmd not supported in spi */
>>  		dev_dbg(&mci->dev, "Select the card, and put it into Transfer Mode\n");
>>  		/* Select the card, and put it into Transfer Mode */
>> diff --git a/include/mci.h b/include/mci.h
>> index 0f10e8a..d3a553e 100644
>> --- a/include/mci.h
>> +++ b/include/mci.h
>> @@ -294,6 +294,8 @@ struct mci_host {
>>  	unsigned clock;		/**< Current clock used to talk to the card */
>>  	unsigned bus_width;	/**< used data bus width to the card */
>>  	unsigned max_req_size;
>> +	unsigned dsr_val;	/**< optional dsr value */
>> +	int use_dsr;		/**< optional dsr usage flag */
>>  
>>  	/** init the host interface */
>>  	int (*init)(struct mci_host*, struct device_d*);
>> @@ -344,6 +346,7 @@ struct mci {
>>  	unsigned write_bl_len;
>>  	uint64_t capacity;	/**< Card's data capacity in bytes */
>>  	int ready_for_use;	/** true if already probed */
>> +	int dsr_imp;		/**< DSR implementation state from CSD */
>>  	char *ext_csd;
>>  	int probe;
>>  	struct param_d *param_probe;
>> -- 
>> 1.7.9.5
>>
>>
> 


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