Re: [PATCH] mmc: mmc: Fix HS switch failure in mmc_select_hs400()

[Ziyuan Xu <xzy.xu@rock-chips.com>]

On 2016年05月26日 17:06, Adrian Hunter wrote:
> On 26/05/16 08:50, Ziyuan Xu wrote:
>> To slove the issue which was found on gru board for hs400.
>>
>> [    4.616946] sdhci: Secure Digital Host Controller Interface driver
>> [    4.623135] sdhci: Copyright(c) Pierre Ossman
>> [    4.722575] sdhci-pltfm: SDHCI platform and OF driver helper
>> [    4.730962] sdhci-arasan fe330000.sdhci: No vmmc regulator found
>> [    4.737444] sdhci-arasan fe330000.sdhci: No vqmmc regulator found
>> [    4.774930] mmc0: SDHCI controller on fe330000.sdhci [fe330000.sdhci] using ADMA
>> [    4.980295] mmc0: switch to high-speed from hs200 failed, err:-84
>> [    4.986487] mmc0: error -84 whilst initialising MMC card
>>
>> We should change HS400 mode selection timing to meet JEDEC
>> specification. The JEDEC 5.1 said that change the frequency to <= 52MHZ
>> after HS_TIMING switch. Refer to section 6.6.2.3 "HS400" timing mode
>> selection:
>> Set the "Timing Interface" parameter in the HS_TIMING[185] field of the
>> Extended CSD register to 0x1 to switch to High Speed mode and then set
>> the clock frequency to a value not greater than 52MHZ.
> Do you need a fix also for re-tuning? i.e. does re-tuning work with this
> patch? Or do you not need re-tuning?

Do you mean that revise the similar timing in mmc_hs400_to_hs200()as 
shown below?

diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
index 8e4d059..4232a42 100644
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1161,10 +1161,6 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
         if (host->caps & MMC_CAP_WAIT_WHILE_BUSY)
                 send_status = false;

-       /* Reduce frequency to HS */
-       max_dtr = card->ext_csd.hs_max_dtr;
-       mmc_set_clock(host, max_dtr);
-
         /* Switch HS400 to HS DDR */
         val = EXT_CSD_TIMING_HS;
         err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
@@ -1175,6 +1171,10 @@ int mmc_hs400_to_hs200(struct mmc_card *card)

         mmc_set_timing(host, MMC_TIMING_MMC_DDR52);

+       /* Reduce frequency to HS */
+       max_dtr = card->ext_csd.hs_max_dtr;
+       mmc_set_clock(host, max_dtr);
+
         if (!send_status) {
                 err = mmc_switch_status(card);
                 if (err)

The spec doesn't require mode selection from hs400 to hs200, moreover I 
have not yet hit any failure in mmc_hs400_to_hs200.
Thus I don't know whether a fix is needed for re-tuning.
By the way, what's your opinion for this patch?   I know, you did it on 
purpose that I found some message from git log.

>> Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
>> ---
>>   drivers/mmc/core/mmc.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>> index b81b08f..8e4d059 100644
>> --- a/drivers/mmc/core/mmc.c
>> +++ b/drivers/mmc/core/mmc.c
>> @@ -1078,10 +1078,6 @@ static int mmc_select_hs400(struct mmc_card *card)
>>   	if (host->caps & MMC_CAP_WAIT_WHILE_BUSY)
>>   		send_status = false;
>>   
>> -	/* Reduce frequency to HS frequency */
>> -	max_dtr = card->ext_csd.hs_max_dtr;
>> -	mmc_set_clock(host, max_dtr);
>> -
>>   	/* Switch card to HS mode */
>>   	val = EXT_CSD_TIMING_HS;
>>   	err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>> @@ -1097,6 +1093,10 @@ static int mmc_select_hs400(struct mmc_card *card)
>>   	/* Set host controller to HS timing */
>>   	mmc_set_timing(card->host, MMC_TIMING_MMC_HS);
>>   
>> +	/* Reduce frequency to HS frequency */
>> +	max_dtr = card->ext_csd.hs_max_dtr;
>> +	mmc_set_clock(host, max_dtr);
>> +
>>   	if (!send_status) {
>>   		err = mmc_switch_status(card);
>>   		if (err)
>>
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