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SubjectRe: [PATCH V4 2/2] mmc: sdhci-msm: support voltage pad switching
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On 3/29/2018 4:23 AM, Doug Anderson wrote:
> Hi,
>
> On Wed, Mar 28, 2018 at 6:08 AM, Vijay Viswanath
> <vviswana@codeaurora.org> wrote:
>> From: Krishna Konda <kkonda@codeaurora.org>
>>
>> The PADs for SD card are dual-voltage that support 3v/1.8v. Those PADs
>> have a control signal (io_pad_pwr_switch/mode18 ) that indicates
>> whether the PAD works in 3v or 1.8v.
>>
>> SDHC core on msm platforms should have IO_PAD_PWR_SWITCH bit set/unset
>> based on actual voltage used for IO lines. So when power irq is
>> triggered for io high or io low, the driver should check the voltages
>> supported and set the pad accordingly.
>>
>> Signed-off-by: Krishna Konda <kkonda@codeaurora.org>
>> Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
>> Signed-off-by: Vijay Viswanath <vviswana@codeaurora.org>
>> ---
>> drivers/mmc/host/sdhci-msm.c | 64 ++++++++++++++++++++++++++++++++++++++++++--
>> 1 file changed, 62 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
>> index 2fcd9010..bbf9626 100644
>> --- a/drivers/mmc/host/sdhci-msm.c
>> +++ b/drivers/mmc/host/sdhci-msm.c
>> @@ -78,12 +78,15 @@
>> #define CORE_HC_MCLK_SEL_DFLT (2 << 8)
>> #define CORE_HC_MCLK_SEL_HS400 (3 << 8)
>> #define CORE_HC_MCLK_SEL_MASK (3 << 8)
>> +#define CORE_IO_PAD_PWR_SWITCH_EN (1 << 15)
>> +#define CORE_IO_PAD_PWR_SWITCH (1 << 16)
>> #define CORE_HC_SELECT_IN_EN BIT(18)
>> #define CORE_HC_SELECT_IN_HS400 (6 << 19)
>> #define CORE_HC_SELECT_IN_MASK (7 << 19)
>>
>> #define CORE_3_0V_SUPPORT (1 << 25)
>> #define CORE_1_8V_SUPPORT (1 << 26)
>> +#define CORE_VOLT_SUPPORT (CORE_3_0V_SUPPORT | CORE_1_8V_SUPPORT)
>>
>> #define CORE_CSR_CDC_CTLR_CFG0 0x130
>> #define CORE_SW_TRIG_FULL_CALIB BIT(16)
>> @@ -1109,7 +1112,7 @@ static void sdhci_msm_handle_pwr_irq(struct sdhci_host *host, int irq)
>> u32 irq_status, irq_ack = 0;
>> int retry = 10;
>> u32 pwr_state = 0, io_level = 0;
>> -
>> + u32 config;
>>
>> irq_status = readl_relaxed(msm_host->core_mem + CORE_PWRCTL_STATUS);
>> irq_status &= INT_MASK;
>> @@ -1166,6 +1169,45 @@ static void sdhci_msm_handle_pwr_irq(struct sdhci_host *host, int irq)
>> */
>> writel_relaxed(irq_ack, msm_host->core_mem + CORE_PWRCTL_CTL);
>>
>> + /*
>> + * If we don't have info regarding the voltage levels supported by
>> + * regulators, don't change the IO PAD PWR SWITCH.
>> + */
>> + if (msm_host->caps_0 & CORE_VOLT_SUPPORT) {
>> + /* Ensure order between core_mem and hc_mem */
>> + mb();
>
> Like in v2, I don't understand why you need a mb() before the read
> from CORE_VENDOR_SPEC. No reads or writes to the core_mem will affect
> the value you're reading here, so you need no barrier.
>
> If you need a barrier before the _write_ to CORE_VENDOR_SPEC then add
> it below. Then in the case where the config doesn't change you have
> no barriers.
>
>
>> + /*
>> + * We should unset IO PAD PWR switch only if the register write
>> + * can set IO lines high and the regulator also switches to 3 V.
>> + * Else, we should keep the IO PAD PWR switch set.
>> + * This is applicable to certain targets where eMMC vccq supply
>> + * is only 1.8V. In such targets, even during REQ_IO_HIGH, the
>> + * IO PAD PWR switch must be kept set to reflect actual
>> + * regulator voltage. This way, during initialization of
>> + * controllers with only 1.8V, we will set the IO PAD bit
>> + * without waiting for a REQ_IO_LOW.
>> + */
>
> For the above comment, what about just:
>
> new_config = config
> if (msm_host->caps_0 == CORE_1_8V_SUPPORT) {
> new_config |= CORE_IO_PAD_PWR_SWITCH;
> } else if (msm_host->caps_0 == CORE_3_3V_SUPPORT) {
> new_config &= ~CORE_IO_PAD_PWR_SWITCH;
> } else if (msm_host->caps_0 & CORE_VOLT_SUPPORT) {
> if (io_level & REQ_IO_HIGH)
> new_config &= ~CORE_IO_PAD_PWR_SWITCH;
> else if (io_level & REQ_IO_LOW)
> new_config |= CORE_IO_PAD_PWR_SWITCH;
> }

This looks a big mess of if/else. Does the above implementation have
better performance compared to having two if/else with bit operations
inside ? The latter looks much cleaner and faster.

If regulator only supports 3V and we get a io_low from BUS_OFF (
REQ_IO_LOW should never come if we don't support 1.8V), it is ok to set
io pad.

> if (config != new_config) {
> ...
> }
>
> AKA: first check if it only supports one voltage and pick that one.
> Else if it supports both you can use the request. This might be more
> important if you get rid of the initial setting in
> sdhci_msm_set_regulator_caps() as I'm suggesting.
>
>
>> + config = readl_relaxed(host->ioaddr + CORE_VENDOR_SPEC);
>> +
>> + if (((io_level & REQ_IO_HIGH) && (msm_host->caps_0 &
>> + CORE_3_0V_SUPPORT)) &&
>> + (config & CORE_IO_PAD_PWR_SWITCH)) {
>> + config &= ~CORE_IO_PAD_PWR_SWITCH;
>> + writel_relaxed(config,
>> + host->ioaddr + CORE_VENDOR_SPEC);
>> + /* IO PAD register is in different memory space */
>> + mb();
>
> Wow, for a driver that tries so hard to use "relaxed" versions of
> writes to avoid barriers you sure end up needing to sprinkle a lot of
> these around "just in case". :( ...this one seems extra fishy
> because:
>
> * There are no more accesses after this one in this function.
>
> * If you're worried about something that happens outside of the
> context of the IRQ needing this wb() then that's a silly concern.
> Presumably if they were doing anything that could race with you they'd
> have a lock and locking routines are implicit barriers.
>
> * In the context of the IRQ itself the next call is
> sdhci_msm_complete_pwr_irq_wait(), which eventually calls wake_up.
> This has a locking primitive and thus an implicit barrier.
>

Sorry, I didn't get implicit barrier in locking primitive.
In mmc_set_signal_voltage switch:
1. Send cmd 11.
2. Switch 1.8V in SDHCI_HOST_CONTROL2
3. Wait for pwr_irq wake_up().
4. pwr_irq context comes up & does register read/writes in core mem.
Updates IO PAD in HC mem.
5. pwr_irq calls wake_up.
6. mmc_set_signal_voltage_switch context does further register
read/writes which expects IO_PAD change within pwr_irq context is
complete before step 6.

Can wake_up() ensure that any update to CORE_VENDOR_SPEC happens before
any register writes in HC after the wake_up() ?

> * There's a direct call of sdhci_msm_handle_pwr_irq() from probe, and
> it has a big fat mb(). I have a hard time believing that matters too
> because I'd bet "platform_get_irq_byname" has at least one lock in it.
>
>
> IMHO these "_relaxed" calls are just not worth it except in _very_
> targeted usage.
>
>
>> + } else if (((io_level & REQ_IO_LOW) ||
>> + (msm_host->caps_0 & CORE_1_8V_SUPPORT)) &&
>> + !(config & CORE_IO_PAD_PWR_SWITCH)) {
>> + config |= CORE_IO_PAD_PWR_SWITCH;
>> + writel_relaxed(config,
>> + host->ioaddr + CORE_VENDOR_SPEC);
>> + /* IO PAD bit is in different memory space */
>> + mb();
>> + }
>> + }
>> +
>> if (pwr_state)
>> msm_host->curr_pwr_state = pwr_state;
>> if (io_level)
>> @@ -1322,7 +1364,8 @@ static int sdhci_msm_set_regulator_caps(struct sdhci_msm_host *msm_host)
>> {
>> struct mmc_host *mmc = msm_host->mmc;
>> struct regulator *supply = mmc->supply.vqmmc;
>> - u32 caps = 0;
>> + u32 caps = 0, config;
>> + struct sdhci_host *host = mmc_priv(mmc);
>>
>> if (!IS_ERR(mmc->supply.vqmmc)) {
>> if (regulator_is_supported_voltage(supply, 1700000, 1950000))
>> @@ -1335,6 +1378,23 @@ static int sdhci_msm_set_regulator_caps(struct sdhci_msm_host *msm_host)
>> mmc_hostname(mmc), __func__);
>> }
>>
>> + if (caps) {
>> + /*
>> + * Set the PAD_PWR_SWITCH_EN bit so that the PAD_PWR_SWITCH
>> + * bit can be used as required later on.
>> + */
>> + u32 io_level = msm_host->curr_io_level;
>> +
>> + config = readl_relaxed(host->ioaddr + CORE_VENDOR_SPEC);
>> + config |= CORE_IO_PAD_PWR_SWITCH_EN;
>> +
>> + if ((io_level & REQ_IO_HIGH) && (caps & CORE_3_0V_SUPPORT))
>
> Slight nit that there's a tab character after "caps &". Please
> replace it with a space.
>
>

Will do

>> + config &= ~CORE_IO_PAD_PWR_SWITCH;
>> + else if ((io_level & REQ_IO_LOW) || (caps & CORE_1_8V_SUPPORT))
>> + config |= CORE_IO_PAD_PWR_SWITCH;
>
> Are you sure that's right? In English:
>
> * If we requested high and we support high then set to high.
> * else if we requested low __or__ we support low then set low.
>
> Things that are weird above that:
>
> * If we request low but don't support low, switch to low anyway.

> * If we request high but only support low, switch to low anyway.
>
> If nothing else seems like this would deserve a comment, but I'd be
> curious of the justification for that logic.
>
>
> Also: seems like this is duplicated code between here and
> sdhci_msm_handle_pwr_irq(). Does it even need to be here? Can't you
> just move the call to sdhci_msm_set_regulator_caps() before the call
> to sdhci_msm_handle_pwr_irq() in probe? Then just let that first call
> to to sdhci_msm_handle_pwr_irq() do this work? In
> sdhci_msm_handle_pwr_irq() you can always just "OR" in
> CORE_IO_PAD_PWR_SWITCH_EN
>
>
> -Doug
> --


If we don't support 1.8V, then the only time io_low will happen is
during BUS_OFF. For BUS_OFF, enabling IO_PAD_PWR_SWITCH is ok.

This logic is same as what is there in pwr_irq. Added the same stuff
here because by the time we get regulator info from mmc layer, some
power irqs would have already come and gone.


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