[U-Boot] [PATCH V2] mmc: seperate block number into small parts for multi-write cmd

[Lei Wen]

On Mon, Oct 11, 2010 at 5:22 PM, Wolfgang Denk <wd at denx.de> wrote:
> Dear Reinhard Meyer,
>
> In message <4CB2D225.6020702 at emk-elektronik.de> you wrote:
>>
>> After thinking alot about this:
>> Preface: (for understanding of the issue)
>
> Thanks!!
>
>> I see two possible solutions for that problem here:
>> 1. generally limit the number of blocks requested to 65535. The performance
>> penalty for that is insignificant. (65535 blocks are about 32 MiB)
>> 2. limit it on a case by case basis by passing such limit like a host
>> capability to the high level part.
>>
>> Here I would (after much deliberation) favour version 1.
>
> I agree. Implementing 2) is not worth the effort or the code. 32 MiB
> should be enough in most practical cases, and even for really big
> transfers it is a more than appropriate chunk size.
>
>> The second and more serious problem Lei Wen seems to have with his hardware
>> is that DMA seems problematic (how so?) for more than 512 KiB.
>
> Indeed. So far it is totally unclear to me what sort of restriction
> this actually is.  If my interpretation is correct, than such DMA
> transfers should not cross 512 KiB memory boundaries, so the maximum
> transfer size is 512 KiB, but only when you start on a 512 KiB
> aligned address.  Also my interpretation is that this is not actually
> a hard restriction, but only a convenience to avoid handling some DMA
> interrupt properly - in Linux.  I wonder if this really applied to
> U-Boot at all, where we use polling instead.
>
>> I really don't see that we should pull such (unusual?) limitations into the
>> high level part. I think the low level driver could issue several DMA
>> transfers in that case.
>
> Again I agree. thi is a low-level, controller specific detail, which
> should not affect any upper-layer code. It should be completely hidden
> in the controller specific driver code.
>
>> We need concensus here first before we can issue and comment patches.
>
> I think both of us agree. We just need to convince Lei Wen...

Ok, I am also fine with not include the 512KiB restriction.
So we comes to a conclusion that we still use v1 patch, but cut the
512KiB limitation?

Best regards,
Lei