linux-kernel - Re: [PATCH] mmc: dw_mmc: use resource_size

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Message-ID: <CAHp75VdFun5aLxLxau9SN_V+_aF+z2M7pvL9Cjui-i+jN-CUCg@mail.gmail.com>
Date:	Wed, 18 Nov 2015 20:10:25 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] mmc: dw_mmc: use resource_size_t to store physical address

On Wed, Nov 18, 2015 at 6:22 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wednesday 18 November 2015 18:17:32 Andy Shevchenko wrote:
>> On Wed, Nov 18, 2015 at 5:45 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> > On Wednesday 18 November 2015 17:29:19 Andy Shevchenko wrote:
>
>> >> 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
>
> That classification is oversimplified, as the DMA address space
> is often not the same as physical.
>

>> dma_addr_t is a physical address wrt DMA mask.
>>
>> Correct?
>
> dma_addr_t is how a device sees RAM, it is limited by the DMA mask
> that is a subset of the capabilities of the device and the buses
> through which it is connected, and is subject to IOMMU translation
> and possible platform or bus specific offsets from the physical
> memory. I still don't know where you're getting with this.

This is off the review already. I'm just structuring knowledge in my head.
In principle I agree with your patch.


-- 
With Best Regards,
Andy Shevchenko
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