Re: [PATCH] mmc: enable UHS voltage switch for SDSC if supported【请注意，邮件由linux-mmc-owner@xxxxxxxxxxxxxxx代发】

[Christian Löhle]

Claiming UHS-I support with SDSC is pretty rare, for obvious reasons (namely they are non-standard, so it's a gamble if a host makes use of it), but here you go:
https://de.rs-online.com/web/p/micro-sd-karten/8743910/
(sorry for the german, the site has a en. subpage, but it's certificate seem untrusted.)
The more likely case is that they do not advertise UHS-I to customers,
but the card will show support to the host.
Let's look at this product, just as an example.
https://www.tme.eu/html/EN/goodram-industrial-industrial-sd-sd-micro-memory-cards/ramka_15242_EN_pelny.html
They provide an MLC and pSLC version of each device, with half the capacity naturally.
The 4GB MLC claims UHS-I support, the 2GB pSLC is very likely to be the same controller,
it only claims Class 6.
So either they specifically changed the firmware to remove any UHS support indication,
or, more likely IMO, the card still reports UHS support to the host.
Such a card would benefit from this patch.

Disclaimer: I do not own the product and have not confirmed this device in any way,
but I have seen UHS support on other devices that do not advertise it for their
SDSC versions.
If the mailing list would be interested, I can try to acquire such devices, listed in
public open stores. Modern, potentially UHS supporting cards. are,
as mentioned in the initial Mail, often SLC or pSLC and often are made on
a customers request.


From: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
Sent: Friday, April 23, 2021 3:34 AM
To: Christian Löhle <CLoehle@xxxxxxxxxxxxxx>
Cc: shawn.lin@xxxxxxxxxxxxxx <shawn.lin@xxxxxxxxxxxxxx>; pali@xxxxxxxxxx <pali@xxxxxxxxxx>; huyue2@xxxxxxxxxx <huyue2@xxxxxxxxxx>; tiantao6@xxxxxxxxxxxxx <tiantao6@xxxxxxxxxxxxx>; linux-mmc@xxxxxxxxxxxxxxx <linux-mmc@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx <linux-kernel@xxxxxxxxxxxxxxx>; ulf.hansson@xxxxxxxxxx <ulf.hansson@xxxxxxxxxx>
Subject: Re: [PATCH] mmc: enable UHS voltage switch for SDSC if supported【请注意，邮件由linux-mmc-owner@xxxxxxxxxxxxxxx代发】 
 
On 2021/4/22 21:18, Christian Löhle wrote:
> Ignore the reported capacity if the card otherwise reports UHS support.
> 
> Currently SDSC cards reporting UHS support except for the CCS do not run
> through the voltage switch.
> While strictly speaking a SDSC card cannot support UHS in compliance
> with the standard, there is no good reason to throttle them that way.
> Especially for pSLCs in practice such cards benefit greatly by this patch,

Cduld you provide some more infomation about the SDSC cards which ones 
are labeled as UHS, e.g brand, webpage....

> as they can be new and UHS supporting, but must not lie about their CCS.
> The behaviour of linux-mmc for SDSC is deviating from the standard anyway
> in such a case, as the card is treated as UHS card not supporting the
> voltage switch in general.
> Such a card will come up as
> mmc0: new ultra high speed SDR25 SD card at address 0001.
> Thus the subsystem will support CMD23 and others to the card.
> But if we deviate from the standard anyway, then we might as well
> not throttle SDSC to 25MB/s.
> 
> Signed-off-by: Christian Loehle <cloehle@xxxxxxxxxxxxxx>
> ---
>   drivers/mmc/core/sd.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> index 6fa51a6ed058..281ca2da8e0b 100644
> --- a/drivers/mmc/core/sd.c
> +++ b/drivers/mmc/core/sd.c
> @@ -841,11 +841,10 @@ int mmc_sd_get_cid(struct mmc_host *host, u32 ocr, u32 *cid, u32 *rocr)
>                return err;
>   
>        /*
> -      * In case CCS and S18A in the response is set, start Signal Voltage
> -      * Switch procedure. SPI mode doesn't support CMD11.
> +      * In case S18A in the response is set, start Signal Voltage Switch
> +      * procedure. SPI mode doesn't support CMD11.
>         */
> -     if (!mmc_host_is_spi(host) && rocr &&
> -        ((*rocr & 0x41000000) == 0x41000000)) {
> +     if (!mmc_host_is_spi(host) && rocr && (*rocr & 0x01000000)) {
>                err = mmc_set_uhs_voltage(host, pocr);
>                if (err == -EAGAIN) {
>                        retries--;
> 


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