Re: [PATCH 4/8] env: Rename SYS_MMC_ENV_DEV to ENV_SDMMC_DEVICE_INDEX

[Quentin Schulz <quentin.schulz@cherry.de>]

Hi Marek,

On 3/26/25 2:37 AM, Marek Vasut wrote:
> On 3/26/25 1:15 AM, Tom Rini wrote:
>> On Wed, Mar 26, 2025 at 12:02:08AM +0100, Marek Vasut wrote:
>>> On 3/24/25 1:39 PM, Quentin Schulz wrote:
>>>> Hi Marek,
>>>
>>> Hi,
>>>
>>>> On 3/22/25 10:55 PM, Marek Vasut wrote:
>>>>> Rename the variable and add ENV_ prefix, so that all configuration
>>>>> options which are related to environment would have an CONFIG_ENV_
>>>>> prefix. No functional change.
>>>>>
>>>>> Use ENV_SDMMC_DEVICE_INDEX to clarify this is the SD/MMC device
>>>>> index, a number, as enumerated by U-Boot. Update the help text
>>>>> accordingly.
>>>>>
>>>>
>>>> I disagree with this part of the rename (MMC->SDMMC), our drivers all
>>>> are using mmc (env/mmc.*, drivers/mmc/*, cmd/mmc.c, ...) for both SD 
>>>> and
>>>> MMC. We also have ENV_IS_IN_MMC which is for both. I don't think it's
>>>> worth the confusion.
>>>
>>> My main problem is, that it is confusing to call everything _mmc_ 
>>> even if
>>> most of it also applies to SD . There is no way to discern parts 
>>> which are
>>> MMC specific from parts which are common to SD and MMC now.
>>
>> Do we have support for anything using the MMC part of the standard that
>> is not storage? I certainly agree it's confusingly named atm, but I
>> think changing some parts but not other parts will make it worse, not
>> better.
> That's not what I am concerned about. What I am concerned about is that 
> we are talking about partitions, and only eMMC supports HW partitions, 
> but both SD and MMC support SW partitions . So we should refer to 
> CONFIG_..._SDMMC_..._SW_PARTITION here when talking about SW 
> partitions , but CONFIG_..._MMC_..._HW_PARTITION when talking about eMMC 
> HW partitions. Currently we are missing the two and it yields a horrid 
> confusion. That is in fact what prompted this series.

But the controllers handling SD cards or eMMC are both called mmc in 
device tree and in U-Boot (see mmc command). So for me, MMC covers both. 
As a matter of fact, the mmc command also handles the boot partition 
that is specific to eMMC.

Quite interestingly, the MMC (MultiMediaCard) Wikipedia page starts with

"Not to be confused with SD card or eMMC" and then the first sentence in 
the history section is "The latest version of the eMMC standard", c.f. 
https://en.wikipedia.org/wiki/MultiMediaCard

So essentially, I'm wondering:
- if boot partitions are specific to eMMC and not simpy MMC (and are not 
part of SD card). I know eMMC has a separate standard than MMC.
- if there are other things than eMMC (and SD cards) that are supported 
by the MMC subsystem (outside of the embedded world). It seems like this 
is taking the MMC = eMMC shortcut that I'm not sure is correct?

To add to the confusion, Rockchip often has MMC controllers named SDMMC 
(and their use varies depending on the SoC, sometimes for SD, sometimes 
for eMMC, sometimes for SDIO).

Cheers,
Quentin