Re: [PATCH 6/10] mmc: sdhci-xenon: Add Marvell Xenon SDHC core functionality

[Ziji Hu <huziji@marvell.com>]

Hi Adrian,

On 2016/10/12 21:07, Adrian Hunter wrote:
> On 12/10/16 14:58, Ziji Hu wrote:
>> Hi Adrian,
>>
>> 	Thank you very much for your review.
>> 	I will firstly fix the typo.
>>
>> On 2016/10/11 20:37, Adrian Hunter wrote:
<snip>
>>>> +
>>>> +static int xenon_start_signal_voltage_switch(struct mmc_host *mmc,
>>>> +					     struct mmc_ios *ios)
>>>> +{
>>>> +	struct sdhci_host *host = mmc_priv(mmc);
>>>> +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>>>> +	struct sdhci_xenon_priv *priv = sdhci_pltfm_priv(pltfm_host);
>>>> +
>>>> +	/*
>>>> +	 * Before SD/SDIO set signal voltage, SD bus clock should be
>>>> +	 * disabled. However, sdhci_set_clock will also disable the Internal
>>>> +	 * clock in mmc_set_signal_voltage().
>>>> +	 * If Internal clock is disabled, the 3.3V/1.8V bit can not be updated.
>>>> +	 * Thus here manually enable internal clock.
>>>> +	 *
>>>> +	 * After switch completes, it is unnecessary to disable internal clock,
>>>> +	 * since keeping internal clock active obeys SD spec.
>>>> +	 */
>>>> +	enable_xenon_internal_clk(host);
>>>> +
>>>> +	if (priv->card_candidate) {
>>>
>>> mmc_power_up() calls __mmc_set_signal_voltage() calls
>>> host->ops->start_signal_voltage_switch so priv->card_candidate could be an
>>> invalid reference to an old card.
>>>
>>> So that's not going to work if the card changes - not only for removable
>>> cards but even for eMMC if init fails and retries.
>>>
>> 	As you point out, this piece of code have defects, even though it actually works on Marvell multiple platforms, unless eMMC card is removable.
>>
>> 	I can add a property to explicitly indicate eMMC type in DTS.
>> 	Then card_candidate access can be removed here.
>> 	Does it sounds more reasonable to you?
> 
> Sure
> 
>>
>>>> +		if (mmc_card_mmc(priv->card_candidate))
>>>> +			return xenon_emmc_signal_voltage_switch(mmc, ios);
>>>
>>> So if all you need to know is whether it is a eMMC, why can't DT tell you?
>>>
>> 	I can add an eMMC type property in DTS, to remove the card_candidate access here.
>>
>>>> +	}
>>>> +
>>>> +	return sdhci_start_signal_voltage_switch(mmc, ios);
>>>> +}
>>>> +
>>>> +/*
>>>> + * After determining which slot is used for SDIO,
>>>> + * some additional task is required.
>>>> + */
>>>> +static void xenon_init_card(struct mmc_host *mmc, struct mmc_card *card)
>>>> +{
>>>> +	struct sdhci_host *host = mmc_priv(mmc);
>>>> +	u32 reg;
>>>> +	u8 slot_idx;
>>>> +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
>>>> +	struct sdhci_xenon_priv *priv = sdhci_pltfm_priv(pltfm_host);
>>>> +
>>>> +	/* Link the card for delay adjustment */
>>>> +	priv->card_candidate = card;
>>>
>>> You really need a better way to get the card.  I suggest you take up the
>>> issue with Ulf.  One possibility is to have mmc core set host->card = card
>>> much earlier.
>>>
>> 	Could you please tell me if any issue related to card_candidate still exists, after the card_candidate is removed from xenon_start_signal_voltage_switch() in above?
>> 	It seems that when init_card is called, the structure card has already been updated and stable in MMC/SD/SDIO initialization sequence.
>> 	May I keep it here?
> 
> It works by accident rather than by design.  We can do better.
> 
	Could you please tell me some details which are satisfied about card_candidate?

	I must admit that card_candidate in xenon_start_signal_voltage_switch() is imperfect.
	But card_candidate in init_card() and later in set_ios() work by design, rather than by accident. We did a lot of tests on several platforms.
	
	The structure mmc_card passed in here is a stable one. Thus in my very own opinion, it is safe and stable to use mmc_card here.
	card_candidate is used only in card initialization. It is not active in later transfers after initialization is done.
	It will always updated with mmc_card in next card initialization.

>>
>>>> +	/* Set tuning functionality of this slot */
>>>> +	xenon_slot_tuning_setup(host);
>>>> +
>>>> +	slot_idx = priv->slot_idx;
>>>> +	if (!mmc_card_sdio(card)) {
>>>> +		/* Re-enable the Auto-CMD12 cap flag. */
>>>> +		host->quirks |= SDHCI_QUIRK_MULTIBLOCK_READ_ACMD12;
>>>> +		host->flags |= SDHCI_AUTO_CMD12;
>>>> +
>>>> +		/* Clear SDIO Card Inserted indication */
>>>> +		reg = sdhci_readl(host, SDHC_SYS_CFG_INFO);
>>>> +		reg &= ~(1 << (slot_idx + SLOT_TYPE_SDIO_SHIFT));
>>>> +		sdhci_writel(host, reg, SDHC_SYS_CFG_INFO);
>>>> +
>>>> +		if (mmc_card_mmc(card)) {
>>>> +			mmc->caps |= MMC_CAP_NONREMOVABLE;
>>>> +			if (!(host->quirks2 & SDHCI_QUIRK2_NO_1_8_V))
>>>> +				mmc->caps |= MMC_CAP_1_8V_DDR;
>>>> +			/*
>>>> +			 * Force to clear BUS_TEST to
>>>> +			 * skip bus_test_pre and bus_test_post
>>>> +			 */
>>>> +			mmc->caps &= ~MMC_CAP_BUS_WIDTH_TEST;
>>>> +			mmc->caps2 |= MMC_CAP2_HC_ERASE_SZ |
>>>> +				      MMC_CAP2_PACKED_CMD;
>>>> +			if (mmc->caps & MMC_CAP_8_BIT_DATA)
>>>> +				mmc->caps2 |= MMC_CAP2_HS400_1_8V;
>>>> +		}
>>>> +	} else {
>>>> +		/*
>>>> +		 * Delete the Auto-CMD12 cap flag.
>>>> +		 * Otherwise, when sending multi-block CMD53,
>>>> +		 * Driver will set Transfer Mode Register to enable Auto CMD12.
>>>> +		 * However, SDIO device cannot recognize CMD12.
>>>> +		 * Thus SDHC will time-out for waiting for CMD12 response.
>>>> +		 */
>>>> +		host->quirks &= ~SDHCI_QUIRK_MULTIBLOCK_READ_ACMD12;
>>>> +		host->flags &= ~SDHCI_AUTO_CMD12;
>>>
>>> sdhci_set_transfer_mode() won't enable auto-CMD12 for CMD53 anyway, so is
>>> this needed?
>>>
>> 	In Xenon driver, Auto-CMD12 flag is set to enable full support to Auto-CMD feature, both Auto-CMD12 and Auto-CMD23.
>> 	As a result, when Xenon SDHC slot can both support SD and SDIO, Auto-CMD12 is disabled when SDIO card is inserted, and renabled when SD is inserted.
>>
>> 	I recheck the sdhci code to set Auto-CMD bit in Transfer Mode register, in sdhci_set_transfer_mode():
>> 	if (mmc_op_multi(cmd->opcode) || data->blocks > 1)
>> 	As you can see, as long as it is CMD18/CMD25 OR there are multiple data blocks, Auto-CMD field will be set.
>> 	CMD53 doesn't have CMD23. Thus Auto-CMD12 is selected since Auto-CMD12 flag is set.
>> 	Thus I have to clear Auto-CMD12 to avoid issuing Auto-CMD12 in SDIO transfer.
> 
> 
> The code is:
> 
> 	if (mmc_op_multi(cmd->opcode) || data->blocks > 1) {
> 		mode = SDHCI_TRNS_BLK_CNT_EN | SDHCI_TRNS_MULTI;
> 		/*
> 		 * If we are sending CMD23, CMD12 never gets sent
> 		 * on successful completion (so no Auto-CMD12).
> 		 */
> 		if (sdhci_auto_cmd12(host, cmd->mrq) &&
> 		    (cmd->opcode != SD_IO_RW_EXTENDED))
> 			mode |= SDHCI_TRNS_AUTO_CMD12;
> 		else if (cmd->mrq->sbc && (host->flags & SDHCI_AUTO_CMD23)) {
> 			mode |= SDHCI_TRNS_AUTO_CMD23;
> 			sdhci_writel(host, cmd->mrq->sbc->arg, SDHCI_ARGUMENT2);
> 		}
> 	}
> 
> You can see the check for SD_IO_RW_EXTENDED which is CMD53.
> 
	Sorry. I didn't notice CMD53 check was added.
	I introduced this Auto-CMD12 hack since kernel 3.8. It seems that this check is not added in kernel 3.8.
	Thanks for the information. I will remove the Auto-CMD12 hack.

>>
>> 	I just meet a similar issue in RPMB.
>> 	When Auto-CMD12 flag is set, eMMC RPMB access will trigger Auto-CMD12, since CMD25 is in use.
>> 	It will cause RPMB access failed.
> 
> Can you explain more about the RPMB issue.  Doesn't it use CMD23, so CMD12
> wouldn't be used - auto or manually.
> 
	RPMB go through the MMC ioctl routine.
	Unlike normal data transfer, MMC ioctl for RPMB explicitly issues CMD23. When CMD25 is issued, there is neither data->sbc nor Auto-CMD23.
	As a result, sdhci driver will automatically enable Auto-CMD12 for RPMB CMD25 if Auto-CMD12 flag is set.

>>
>> 	One possible solution is to drop Auto-CMD12 support and use Auto-CMD23 only, in Xenon driver.
>> 	May I know you opinion, please?
> 
> I don't use auto-CMD12 because I don't know if it provides any benefit and
> sdhci does not seem to have implemented Auto CMD12 Error Recovery, although
> I have never looked at it closely.
>
	Actually, Auto-CMD23 is always used on our Xenon. Auto-CMD12 is not used at all.
	But since this driver is a general one for all Marvell products, Auto-CMD12 is also supported in case that Auto-CMD23 is not available.