Re: [PATCH RFC 2/2] mmc: sdhci-msm: support voltage pad switching

From: Vijay Viswanath
Date: Thu Feb 08 2018 - 00:19:23 EST



On 2/3/2018 3:21 AM, Bjorn Andersson wrote:
On Thu 18 Jan 00:05 PST 2018, Vijay Viswanath wrote:

From: Krishna Konda <kkonda@xxxxxxxxxxxxxx>

The PADs for sdhc controller 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.


I'll try to find some time to check that this doesn't break 8916 and
8974...again...


Thanks! Btwn, I had tested the code in db410c.

Signed-off-by: Krishna Konda <kkonda@xxxxxxxxxxxxxx>
Signed-off-by: Venkat Gopalakrishnan <venkatg@xxxxxxxxxxxxxx>
Signed-off-by: Vijay Viswanath <vviswana@xxxxxxxxxxxxxx>
---
drivers/mmc/host/sdhci-msm.c | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)

diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
index 5c23e92..f5728a8 100644
--- a/drivers/mmc/host/sdhci-msm.c
+++ b/drivers/mmc/host/sdhci-msm.c
@@ -78,6 +78,8 @@
#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)
@@ -1166,6 +1168,35 @@ static void sdhci_msm_handle_pwr_irq(struct sdhci_host *host, int irq)
*/
writel_relaxed(irq_ack, msm_host->core_mem + CORE_PWRCTL_CTL);
+ /*
+ * SDHC has core_mem and hc_mem device memory and these memory
+ * addresses do not fall within 1KB region. Hence, any update to
+ * core_mem address space would require an mb() to ensure this gets
+ * completed before its next update to registers within hc_mem.
+ */
+ mb();

If you just use writel() instead of writel_relaxed() you don't need to
sprinkle the driver with comments like this. And you really should be
able to just say "Ensure ordering between core_mem and hc_mem writes" if
you really feel like making it explicit.

+ /*
+ * 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.
+ */
+ if ((io_level & REQ_IO_HIGH) && (msm_host->caps_0 & CORE_3_0V_SUPPORT))
+ writel_relaxed((readl_relaxed(host->ioaddr + CORE_VENDOR_SPEC) &
+ ~CORE_IO_PAD_PWR_SWITCH), host->ioaddr +
+ CORE_VENDOR_SPEC);

Please split this up in read, modify and write operations.


Will do

+ else if ((io_level & REQ_IO_LOW) ||
+ (msm_host->caps_0 & CORE_1_8V_SUPPORT))
+ writel_relaxed((readl_relaxed(host->ioaddr + CORE_VENDOR_SPEC) |
+ CORE_IO_PAD_PWR_SWITCH), host->ioaddr +
+ CORE_VENDOR_SPEC);
+ /* Ensure that the IO PAD switches are updated before proceeding */

That's not what "mb()" does, it ensures that any writes that was done
before this line will hit the hardware before any writes that is done
after this line.


Will update the comments.

But again, using writel() would save us from doing this explicitly
throughout the code.

+ mb();
+
if (pwr_state)
msm_host->curr_pwr_state = pwr_state;
if (io_level)
@@ -1518,6 +1549,13 @@ static int sdhci_msm_probe(struct platform_device *pdev)
}
/*
+ * Set the PAD_PWR_SWITCH_EN bit so that the PAD_PWR_SWITCH bit can
+ * be used as required later on.
+ */
+ writel_relaxed((readl_relaxed(host->ioaddr + CORE_VENDOR_SPEC) |
+ CORE_IO_PAD_PWR_SWITCH_EN), host->ioaddr +
+ CORE_VENDOR_SPEC);

Please rewrite as 3 operations.

Do we need to set the pwr switch value as well? Or we're fine relying on
the existing value here?

After the IO_PAD_PWR_SWTCH is enabled, we will call sdhci_msm_handle_pwr_irq. If there is any pending power irq interrupt, that will set the appropriate pwr switch value. Otherwise, an appropriate value will get set during REQ_BUS_ON event.


Regards,
Bjorn
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