Re: [PATCH] mmc: dw_mmc: use resource_size_t to store physical address

[Andy Shevchenko]

On Wed, Nov 18, 2015 at 5:45 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Wednesday 18 November 2015 17:29:19 Andy Shevchenko wrote:
>>
>> I understand most of the things here, what I don't is how a platform
>> is supposed to work if you have the following:
>> a) HW, that uses register space let's say higher than 32-bit;
>> b) DMA engine, which should provide a DMA capability for above HW block;
>> c) dma_addr_t which does not cover the HW register space.
>
> On this platform, the current code is obviously broken, because the pointer
> is 32-bit wide and cannot reach the registers. I assume you agree on that
> part.

Yes.

> With my patch, the 64-bit resource_size_t in dw_mci helps get the
> correct FIFO address to this line:
>
>         cfg.dst_addr = host->phy_regs + fifo_offset;
>
> There, it remains broken because of the dma_addr_t being too short, and
> we also need Linus' patch from https://lkml.org/lkml/2013/4/26/120 in
> addition to mine.

Wow, never applied.

>
>
>> For me it clearly looks like a platform (HW / SW) configuration issue.
>
> I think some people have argued in the past that we should always use
> the same type for dma_addr_t, resource_size_t and phys_addr_t. That
> would certainly fix the problem you describe as well. In practice,
> everyone has that already, and my patch by itself fixes all the
> cases where the FIFO is at a high address and dma_addr_t is already
> 64-bit wide.

Let me summarize.

We have to have classification by address space
1) physical
2) virtual

Therefore
resource_addr_t must be equal to phys_addr_t since it may carry any
possible physical address.

dma_addr_t is a physical address wrt DMA mask.

Correct?

-- 
With Best Regards,
Andy Shevchenko
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