linux-kernel - Re: [PATCH v2 4/7] of: configure the platform device dma parameters

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Message-ID: <53568E4C.3050305@ti.com>
Date:	Tue, 22 Apr 2014 18:44:12 +0300
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Rob Herring <robherring2@...il.com>
CC:	Santosh Shilimkar <santosh.shilimkar@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2 4/7] of: configure the platform device dma parameters

On 04/22/2014 05:44 PM, Rob Herring wrote:
> On Tue, Apr 22, 2014 at 10:09 AM, Grygorii Strashko
> <grygorii.strashko@...com> wrote:
>> Hi Rob,
>>
>> On 04/21/2014 05:58 PM, Rob Herring wrote:
>>> On Sat, Apr 19, 2014 at 9:32 AM, Santosh Shilimkar
>>> <santosh.shilimkar@...com> wrote:
>>>> Retrieve DMA configuration from DT and setup platform device's DMA
>>>> parameters. The DMA configuration in DT has to be specified using
>>>> "dma-ranges" and "dma-coherent" properties if supported.
>>>>
>>>> We setup dma_pfn_offset using "dma-ranges" and dma_coherent_ops
>>>> using "dma-coherent" device tree properties.
>>>>
>>>> The set_arch_dma_coherent_ops macro has to be defined by arch if
>>>> it supports coherent dma_ops. Otherwise, set_arch_dma_coherent_ops() is
>>>> declared as nop.
>
> [...]
>
>>>>
>>>> +       ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
>>>> +       if (ret < 0) {
>>>
>>> Perhaps an error is not the right return for the default case. The
>>> default should probably be dma_addr and paddr equal to 0 and size 4GB.
>>
>> The error code is needed here to properly distinguish the case when
>> there are no "dma-ranges" defined in DT. Also, I think, that
>> of_dma_get_range() shouldn't return any default values - It just
>> has to get data from DT. And the caller should decide what to do
>> with this data and how to handle error cases.
>>
>> So, I prefer to keep behavior as is:
>> - in case of failure of_dma_get_range() will not touch values of
>>    &dma_addr, &paddr, &size.
>
> Fine, but that is not how of_dma_get_range currently behaves:

Yep. That's will be fixed as you've commented :)

>
> +       *dma_addr = of_read_number(ranges, naddr);
> +       *paddr = of_translate_dma_address(np, ranges);
> +       if (*paddr == OF_BAD_ADDR) {
> +               pr_err("%s: translation of DMA address(%pad) to CPU
> address failed node(%s)\n",
> +                      __func__, dma_addr, np->full_name);
> +               ret = -EINVAL;
> +       }
>
> Rob
>

Regards
Grygorii
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