[PATCH 3/3] mmc: sdhci-of-esdhc: add workaround for T4240 incorrect HOSTVER value

[Ulf Hansson]

On 25 July 2015 at 04:27, Scott Wood <scottwood at freescale.com> wrote:
> On Tue, 2015-07-21 at 15:02 +0200, Ulf Hansson wrote:
>> On 21 July 2015 at 11:45, Yangbo Lu <yangbo.lu at freescale.com> wrote:
>> > For T4240-R1.0-R2.0, the HOSTVER register has incorrcet vender
>> > version value and sdhc spec version value. This will break down
>> > the ADMA data transfer. So add workaround to get right value
>> > VVN=0x13, SVN = 0x1.
>>
>> So T4240-R1.0-R2.0 is the version of the controller, right?
>>
>> If I understand correct you are checking what CPU/SoC you are running
>> on, to figure out which controller version you are using, as that
>> can't be fetched (trusted) from the registers of the esdhc controller
>> itself!?
>>
>> Instead, you could deal with this directly in the DTS files. I assume
>> you have some DTS file for each SoC/board variant, right?
>
> No, we do not have a separate DTS file for each revision of an SoC -- and if
> we did, we'd constantly have people using the wrong one.
>
>> In principle, in your DTS file specific for the board/SoC that holds
>> the T4240-R1.0-R2.0 version of the controller, should add a specific
>> esdhc DT property to indicate this errata.
>
> No, because (in addition to the above issue about chip revisions) the device
> tree is stable ABI and errata are often discovered after device trees are
> deployed.

Fair enough. Then what is your suggestion for the solution here?

As I understand it, you can't update the already deployed DTB. Shall
we make Linux patch the DTB during boot instead, depending on the chip
revision?

Kind regards
Uffe