Re: [RFC PATCH 1/1 v8]mmc: Support-FFU-for-eMMC-v5.0

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On 1 September 2014 11:26, Alex Lemberg <Alex.Lemberg@xxxxxxxxxxx> wrote:
> [snip]
>
>> My conclusion from that is (correct me if I am wrong, since it may be vendor
>> specific), that only minor modifications should be needed to the mmc ioctl. We
>> need to add special treatment for when "cmd.opcode ==
>> MMC_FFU_DOWNLOAD_OP". In such scenario the following sequence needs to
>> be maintained.
>>
>> 1. Claim host etc.
>> 2. Set FFU mode.
>> 3. Write some sectors to the FFU area, but in the same way as any other mmc
>> ioctl WRITE is done.
>> 4. Set normal mode.
>> 5. Relase host etc.
>>
>> That sequence then needs to be repeated to write the complete firmware,
>> depending on buffer size. Between each and every piece of FFU data that is
>> written, normal READ/WRITE operations can be served.
>> Right?
>
> We checked again the current IOCTL implementation, and we see issues
> In implementing FFU as suggested above:
>
> 1. No support for multiple Write operations.
>     For running Multiple I/O, user need to send CMD23 or CMD12.
>     So structures "sbc" or "stop" of "mmc_blk_request" should be set accordingly.

You are right regarding multiple I/O!

I suppose using single block write option (CMD24) still can be used
for FFU, right?

Yes, we would suffer from unoptimized performance, but on the other
hand - how much data could we typically be expected to write? Do you
have some rough numbers that you can share?

>
> 2. There is a limit in chunk size in current implementation of IOCTL.
>      From some reason we can't write more than 64KB on our platform,
>      Although, the MMC_IOC_MAX_BYTES is defined to be 128KB

That is likely because the mmc host driver may limit the size, due to
it's controller HW.

>
> Based on this, we think that using existing IOCTL implementation is not
> a good solution for FFU.

Okay, let's for now continue with your current approach and try to
address those concerns I have raised while reviewing the code. I will
happily review new versions of the patch(es).

Kind regards
Uffe
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