[PATCH 0/2] Validate and clean up UHS/DDR/HS200 timing checks

[PATCH 0/2] Validate and clean up UHS/DDR/HS200 timing checks

[Shawn Lin]

This series adds validation for UHS/DDR/HS200 timing modes when the host
only supports 1-bit bus width which also fixes a real performance drop issue
due to incorrect hs200 mode switch code. And then cleans up the check in
mmc_host_can_uhs().


Luke Wang (1):
  mmc: core: Validate UHS/DDR/HS200 timing selection for 1-bit bus width

Shawn Lin (1):
  mmc: core: Remove checking MMC_CAP_4_BIT_DATA from mmc_host_can_uhs()

 drivers/mmc/core/host.c | 9 +++++++++
 drivers/mmc/core/host.h | 6 +-----
 2 files changed, 10 insertions(+), 5 deletions(-)

-- 
2.7.4

[PATCH 1/2] mmc: core: Validate UHS/DDR/HS200 timing selection for 1-bit bus width

[Shawn Lin]

From: Luke Wang <ziniu.wang_1@nxp.com>

UHS/DDR/HS200 modes require at least 4-bit bus support. Host controllers
that lack relevant capability registers rely on paring properties provided
by firmware, which may incorrectly set these modes. Now that mmc_validate_host_caps()
has been introduced to validate such configuration violations, let's also
add checks for UHS/DDR/HS200 modes.

This fixes an issue where, if the HS200/HS400 property is set while only a
1-bit bus width is used, mmc_select_hs200() returns 0 without actually performing
the mode switch. Consequently, mmc_select_timing() proceeds without falling back to
mmc_select_hs(), leaving the eMMC device operating in legacy mode (26 MHz) instead
of switching to High Speed mode (52 MHz).

Signed-off-by: Luke Wang <ziniu.wang_1@nxp.com>
[Shawn: reword the commit msg and drop HS400 change]
Signed-off-by: Shawn Lin <shawn.lin@linux.dev>
---

 drivers/mmc/core/host.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
index 88c95db..d1d4870 100644
--- a/drivers/mmc/core/host.c
+++ b/drivers/mmc/core/host.c
@@ -624,6 +624,15 @@ static int mmc_validate_host_caps(struct mmc_host *host)
 		return -EINVAL;
 	}
 
+	/* UHS/DDR/HS200 modes require at least 4-bit bus */
+	if (!(caps & (MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA)) &&
+	    ((caps & (MMC_CAP_UHS | MMC_CAP_DDR)) || (caps2 & MMC_CAP2_HS200))) {
+		dev_warn(dev, "drop UHS/DDR/HS200 support since 1-bit bus only\n");
+		host->caps = caps = caps & ~(MMC_CAP_UHS | MMC_CAP_DDR);
+		host->caps2 = caps2 = caps2 & ~MMC_CAP2_HS200;
+	}
+
+	/* HS400 and HS400ES modes require 8-bit bus */
 	if (caps2 & (MMC_CAP2_HS400_ES | MMC_CAP2_HS400) &&
 	    !(caps & MMC_CAP_8_BIT_DATA) && !(caps2 & MMC_CAP2_NO_MMC)) {
 		dev_warn(dev, "drop HS400 support since no 8-bit bus\n");
-- 
2.7.4

[PATCH 2/2] mmc: core: Remove checking MMC_CAP_4_BIT_DATA from mmc_host_can_uhs()

[Shawn Lin]

The bus width support for UHS mode is now validated in mmc_validate_host_caps().
Therefore, we can safely remove the explicit MMC_CAP_4_BIT_DATA check from
mmc_host_can_uhs(). As part of this cleanup, simplify the condition by using the
consolidated MMC_CAP_UHS flag.

Signed-off-by: Shawn Lin <shawn.lin@linux.dev>
---

 drivers/mmc/core/host.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/mmc/core/host.h b/drivers/mmc/core/host.h
index 5941d68..6bce5a4 100644
--- a/drivers/mmc/core/host.h
+++ b/drivers/mmc/core/host.h
@@ -56,11 +56,7 @@ static inline int mmc_host_can_access_boot(struct mmc_host *host)
 
 static inline int mmc_host_can_uhs(struct mmc_host *host)
 {
-	return host->caps &
-		(MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25 |
-		 MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR104 |
-		 MMC_CAP_UHS_DDR50) &&
-	       host->caps & MMC_CAP_4_BIT_DATA;
+	return host->caps & MMC_CAP_UHS;
 }
 
 static inline bool mmc_card_hs200(struct mmc_card *card)
-- 
2.7.4

Re: [PATCH 1/2] mmc: core: Validate UHS/DDR/HS200 timing selection for 1-bit bus width

[Ulf Hansson]

On Fri, 6 Mar 2026 at 13:48, Shawn Lin <shawn.lin@linux.dev> wrote:
>
> From: Luke Wang <ziniu.wang_1@nxp.com>
>
> UHS/DDR/HS200 modes require at least 4-bit bus support. Host controllers
> that lack relevant capability registers rely on paring properties provided
> by firmware, which may incorrectly set these modes. Now that mmc_validate_host_caps()
> has been introduced to validate such configuration violations, let's also
> add checks for UHS/DDR/HS200 modes.
>
> This fixes an issue where, if the HS200/HS400 property is set while only a
> 1-bit bus width is used, mmc_select_hs200() returns 0 without actually performing
> the mode switch. Consequently, mmc_select_timing() proceeds without falling back to
> mmc_select_hs(), leaving the eMMC device operating in legacy mode (26 MHz) instead
> of switching to High Speed mode (52 MHz).
>
> Signed-off-by: Luke Wang <ziniu.wang_1@nxp.com>
> [Shawn: reword the commit msg and drop HS400 change]
> Signed-off-by: Shawn Lin <shawn.lin@linux.dev>
> ---
>
>  drivers/mmc/core/host.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index 88c95db..d1d4870 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -624,6 +624,15 @@ static int mmc_validate_host_caps(struct mmc_host *host)
>                 return -EINVAL;
>         }
>
> +       /* UHS/DDR/HS200 modes require at least 4-bit bus */
> +       if (!(caps & (MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA)) &&
> +           ((caps & (MMC_CAP_UHS | MMC_CAP_DDR)) || (caps2 & MMC_CAP2_HS200))) {
> +               dev_warn(dev, "drop UHS/DDR/HS200 support since 1-bit bus only\n");
> +               host->caps = caps = caps & ~(MMC_CAP_UHS | MMC_CAP_DDR);
> +               host->caps2 = caps2 = caps2 & ~MMC_CAP2_HS200;

Hmm.

How about just updating the temporary variables, caps and caps2, here?

Then at the end of the function when we have validated all "caps", we
can update the variables in the host, like:
host->caps = caps;
host->caps2 = caps2;

> +       }
> +
> +       /* HS400 and HS400ES modes require 8-bit bus */
>         if (caps2 & (MMC_CAP2_HS400_ES | MMC_CAP2_HS400) &&
>             !(caps & MMC_CAP_8_BIT_DATA) && !(caps2 & MMC_CAP2_NO_MMC)) {
>                 dev_warn(dev, "drop HS400 support since no 8-bit bus\n");
> --
> 2.7.4
>

Kind regards
Uffe

Re: [PATCH 1/2] mmc: core: Validate UHS/DDR/HS200 timing selection for 1-bit bus width

[Shawn Lin]

Hi Ulf,

在 2026/03/09 星期一 22:57, Ulf Hansson 写道:
> On Fri, 6 Mar 2026 at 13:48, Shawn Lin <shawn.lin@linux.dev> wrote:
>>
>> From: Luke Wang <ziniu.wang_1@nxp.com>
>>
>> UHS/DDR/HS200 modes require at least 4-bit bus support. Host controllers
>> that lack relevant capability registers rely on paring properties provided
>> by firmware, which may incorrectly set these modes. Now that mmc_validate_host_caps()
>> has been introduced to validate such configuration violations, let's also
>> add checks for UHS/DDR/HS200 modes.
>>
>> This fixes an issue where, if the HS200/HS400 property is set while only a
>> 1-bit bus width is used, mmc_select_hs200() returns 0 without actually performing
>> the mode switch. Consequently, mmc_select_timing() proceeds without falling back to
>> mmc_select_hs(), leaving the eMMC device operating in legacy mode (26 MHz) instead
>> of switching to High Speed mode (52 MHz).
>>
>> Signed-off-by: Luke Wang <ziniu.wang_1@nxp.com>
>> [Shawn: reword the commit msg and drop HS400 change]
>> Signed-off-by: Shawn Lin <shawn.lin@linux.dev>
>> ---
>>
>>   drivers/mmc/core/host.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
>> index 88c95db..d1d4870 100644
>> --- a/drivers/mmc/core/host.c
>> +++ b/drivers/mmc/core/host.c
>> @@ -624,6 +624,15 @@ static int mmc_validate_host_caps(struct mmc_host *host)
>>                  return -EINVAL;
>>          }
>>
>> +       /* UHS/DDR/HS200 modes require at least 4-bit bus */
>> +       if (!(caps & (MMC_CAP_4_BIT_DATA | MMC_CAP_8_BIT_DATA)) &&
>> +           ((caps & (MMC_CAP_UHS | MMC_CAP_DDR)) || (caps2 & MMC_CAP2_HS200))) {
>> +               dev_warn(dev, "drop UHS/DDR/HS200 support since 1-bit bus only\n");
>> +               host->caps = caps = caps & ~(MMC_CAP_UHS | MMC_CAP_DDR);
>> +               host->caps2 = caps2 = caps2 & ~MMC_CAP2_HS200;
> 
> Hmm.
> 
> How about just updating the temporary variables, caps and caps2, here?
> 
> Then at the end of the function when we have validated all "caps", we
> can update the variables in the host, like:
> host->caps = caps;
> host->caps2 = caps2;

It looks better. Will update v2 based on your suggestion.

> 
>> +       }
>> +
>> +       /* HS400 and HS400ES modes require 8-bit bus */
>>          if (caps2 & (MMC_CAP2_HS400_ES | MMC_CAP2_HS400) &&
>>              !(caps & MMC_CAP_8_BIT_DATA) && !(caps2 & MMC_CAP2_NO_MMC)) {
>>                  dev_warn(dev, "drop HS400 support since no 8-bit bus\n");
>> --
>> 2.7.4
>>
> 
> Kind regards
> Uffe
>