linux-kernel - Re: [PATCH] nommu: allow mmap when !CONFIG

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Date:   Fri, 9 Dec 2016 16:47:20 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     Vladimir Murzin <vladimir.murzin@....com>
Cc:     linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Robin.Murphy@....com, Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] nommu: allow mmap when !CONFIG_MMU

2016-12-09 16:36 GMT+01:00 Vladimir Murzin <vladimir.murzin@....com>:
> On 09/12/16 15:27, Benjamin Gaignard wrote:
>> + Vladimir
>
> I'm not in DMA, but I can see that with your patch it deviates from
> dma_common_mmap(), can you give more context, please?

I'm working on ARM platform with MMU (stm32f4) to enable display driver.
Framebuffer is allocated with dma_alloc_wc() and when userland try to mmap
drm/kms fraemwork calls dma_mmap_wc().
All this is in drivers/gpu/drm/drm_gem_cma_helper.c

dma_mmap_wc() call failed because __arm_dma_mmap() always return an
error if CONFIG_MMU
isn't defined.
That what I try to solve with this patch.

> Cheers
> Vladimir
>
>>
>> 2016-12-01 14:48 GMT+01:00 Benjamin Gaignard <benjamin.gaignard@...aro.org>:
>>> commit ab6494f0c96f ("nommu: Add noMMU support to the DMA API") have
>>> add CONFIG_MMU compilation flag but that prohibit to use dma_mmap_wc()
>>> when the platform doesn't have MMU.
>>>
>>> This patch call vm_iomap_memory() in noMMU case to test if addresses
>>> are correct and set wma->vm_flags rather than all return an error.
>>>
>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...aro.org>
>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>> Cc: arnd@...db.de
>>> ---
>>>  arch/arm/mm/dma-mapping.c | 3 +++
>>>  1 file changed, 3 insertions(+)
>>>
>>> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
>>> index ab4f745..230875e 100644
>>> --- a/arch/arm/mm/dma-mapping.c
>>> +++ b/arch/arm/mm/dma-mapping.c
>>> @@ -868,6 +868,9 @@ static int __arm_dma_mmap(struct device *dev, struct vm_area_struct *vma,
>>>                                       vma->vm_end - vma->vm_start,
>>>                                       vma->vm_page_prot);
>>>         }
>>> +#else
>>> +       ret = vm_iomap_memory(vma, vma->vm_start,
>>> +                             (vma->vm_end - vma->vm_start));
>>>  #endif /* CONFIG_MMU */
>>>
>>>         return ret;
>>> --
>>> 1.9.1
>>>
>>
>



-- 
Benjamin Gaignard

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