On 6/10/20 8:24 AM, Christoph Hellwig wrote:
> Ok, I finally found the original patch from Vladimir. Comments below:
>
>> +++ b/kernel/dma/direct.c
>> @@ -456,14 +456,14 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
>> #else /* CONFIG_MMU */
>> bool dma_direct_can_mmap(struct device *dev)
>> {
>> - return false;
>> + return true;
>> }
>>
>> int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
>> void *cpu_addr, dma_addr_t dma_addr, size_t size,
>> unsigned long attrs)
>> {
>> - return -ENXIO;
>> + return vm_iomap_memory(vma, vma->vm_start, (vma->vm_end - vma->vm_start));;
>
> I think we should try to reuse the mmu dma_direct_mmap implementation,
> which does about the same. This version has been compile tested on
> arm-nommu only, let me know what you think: (btw, a nommu_defconfig of
> some kind for arm would be nice..)
Catch-all nommu_defconfig is not easy for ARM, AFAIK folk carry few hacks
for randconfig...
Meanwhile, known working NOMMU configs
$ git grep "# CONFIG_MMU is not set" arch/arm/configs/
arch/arm/configs/efm32_defconfig:# CONFIG_MMU is not set
arch/arm/configs/lpc18xx_defconfig:# CONFIG_MMU is not set
arch/arm/configs/mps2_defconfig:# CONFIG_MMU is not set
arch/arm/configs/stm32_defconfig:# CONFIG_MMU is not set
arch/arm/configs/vf610m4_defconfig:# CONFIG_MMU is not set
>
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index d006668c0027d2..e0dae570a51530 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -71,6 +71,7 @@ config SWIOTLB
> # in the pagetables
> #
> config DMA_NONCOHERENT_MMAP
> + default y if !MMU
> bool
Nit: def_bool !MMU
>
> config DMA_REMAP
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 0a4881e59aa7d6..9ec6a5c3fc578c 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -459,7 +459,6 @@ int dma_direct_get_sgtable(struct device *dev, struct sg_table *sgt,
> return ret;
> }
>
> -#ifdef CONFIG_MMU
> bool dma_direct_can_mmap(struct device *dev)
> {
> return dev_is_dma_coherent(dev) ||
> @@ -485,19 +484,6 @@ int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
> return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
> user_count << PAGE_SHIFT, vma->vm_page_prot);
> }
> -#else /* CONFIG_MMU */
> -bool dma_direct_can_mmap(struct device *dev)
> -{
> - return false;
> -}
> -
> -int dma_direct_mmap(struct device *dev, struct vm_area_struct *vma,
> - void *cpu_addr, dma_addr_t dma_addr, size_t size,
> - unsigned long attrs)
> -{
> - return -ENXIO;
> -}
> -#endif /* CONFIG_MMU */
>
> int dma_direct_supported(struct device *dev, u64 mask)
> {
>
LGTM. FWIW:
Reviewed-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
