linux-kernel - Re: [PATCH] mmc: sdhci: Disable SD card clock before changing parameters

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Message-ID: <6366c08b-1746-4d42-8f2e-af0b27766dbf@intel.com>
Date: Tue, 24 Jun 2025 13:53:27 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Erick Shepherd <erick.shepherd@...com>
CC: <linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>,
	<ulf.hansson@...aro.org>, <gratian.crisan@...rson.com>, Kyle Roeschley
	<kyle.roeschley@...com>, Brad Mouring <brad.mouring@...com>, Jonathan Liu
	<net147@...il.com>
Subject: Re: [PATCH] mmc: sdhci: Disable SD card clock before changing
 parameters

On 19/06/2025 06:29, Jonathan Liu wrote:
> Hi Erick,
> 
> On Tue, 11 Feb 2025 at 15:46, Erick Shepherd <erick.shepherd@...com> wrote:
>>
>> Per the SD Host Controller Simplified Specification v4.20 §3.2.3, change
>> the SD card clock parameters only after first disabling the external card
>> clock. Doing this fixes a spurious clock pulse on Baytrail and Apollo Lake
>> SD controllers which otherwise breaks voltage switching with a specific
>> Swissbit SD card.
>>
>> Signed-off-by: Kyle Roeschley <kyle.roeschley@...com>
>> Signed-off-by: Brad Mouring <brad.mouring@...com>
>> Signed-off-by: Erick Shepherd <erick.shepherd@...com>
>> ---
>>  drivers/mmc/host/sdhci.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index f4a7733a8ad2..5f91b44891f9 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -2065,10 +2065,15 @@ void sdhci_set_clock(struct sdhci_host *host, unsigned int clock)
>>
>>         host->mmc->actual_clock = 0;
>>
>> -       sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
>> +       clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
>> +       if (clk & SDHCI_CLOCK_CARD_EN)
>> +               sdhci_writew(host, clk & ~SDHCI_CLOCK_CARD_EN,
>> +                       SDHCI_CLOCK_CONTROL);
>>
>> -       if (clock == 0)
>> +       if (clock == 0) {
>> +               sdhci_writew(host, 0, SDHCI_CLOCK_CONTROL);
>>                 return;
>> +       }
>>
>>         clk = sdhci_calc_clk(host, clock, &host->mmc->actual_clock);
>>         sdhci_enable_clk(host, clk);
>> --
>> 2.43.0
> 
> This commit is causing eMMC to sometimes fail to detect on my RK3399
> ARM64 board after updating from v5.10.237 to v5.10.238.
> Any ideas?

Looks like this patch will get reverted.

After that, would something like the following work instead?

diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c
index dd084c8750f9..ad95218fe3b3 100644
--- a/drivers/mmc/host/sdhci-pci-core.c
+++ b/drivers/mmc/host/sdhci-pci-core.c
@@ -679,8 +679,19 @@ static int intel_start_signal_voltage_switch(struct mmc_host *mmc,
 	return 0;
 }
 
+static void sdhci_intel_set_clock(struct sdhci_host *host, unsigned int clock)
+{
+	u16 clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+
+	/* Stop card clock separately to avoid glitches on clock line */
+	if (clk & SDHCI_CLOCK_CARD_EN)
+		sdhci_writew(host, clk & ~SDHCI_CLOCK_CARD_EN, SDHCI_CLOCK_CONTROL);
+
+	sdhci_set_clock(host, clock);
+}
+
 static const struct sdhci_ops sdhci_intel_byt_ops = {
-	.set_clock		= sdhci_set_clock,
+	.set_clock		= sdhci_intel_set_clock,
 	.set_power		= sdhci_intel_set_power,
 	.enable_dma		= sdhci_pci_enable_dma,
 	.set_bus_width		= sdhci_set_bus_width,
@@ -690,7 +701,7 @@ static const struct sdhci_ops sdhci_intel_byt_ops = {
 };
 
 static const struct sdhci_ops sdhci_intel_glk_ops = {
-	.set_clock		= sdhci_set_clock,
+	.set_clock		= sdhci_intel_set_clock,
 	.set_power		= sdhci_intel_set_power,
 	.enable_dma		= sdhci_pci_enable_dma,
 	.set_bus_width		= sdhci_set_bus_width,