linux-kernel - Re: [PATCH v5 3/7] drivers: dma-coherent: Account dma_pfn

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Date:   Thu, 22 Jun 2017 13:59:11 +0100
From:   Vladimir Murzin <vladimir.murzin@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux@...linux.org.uk, sza@....hu, arnd@...db.de,
        gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
        alexandre.torgue@...com, robin.murphy@....com,
        benjamin.gaignard@...aro.org, kbuild-all@...org,
        Michal Nazarewicz <mina86@...a86.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Roger Quadros <rogerq@...com>
Subject: Re: [PATCH v5 3/7] drivers: dma-coherent: Account dma_pfn_offset when
 used with device tree

On 20/06/17 14:42, Christoph Hellwig wrote:
> Wouldn't the smal patch below solve the same issue in a simple way?
> 
> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
> index 640a7e63c453..e8f8447d705b 100644
> --- a/drivers/base/dma-coherent.c
> +++ b/drivers/base/dma-coherent.c
> @@ -290,9 +290,11 @@ EXPORT_SYMBOL(dma_mmap_from_coherent);
>  static int rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
>  {
>  	struct dma_coherent_mem *mem = rmem->priv;
> +	dma_addr_t dev_addr = ((rmem->base >> PAGE_SHIFT) -
> +				dev->dma_pfn_offset) << PAGE_SHIFT;
>  
>  	if (!mem &&
> -	    !dma_init_coherent_memory(rmem->base, rmem->base, rmem->size,
> +	    !dma_init_coherent_memory(rmem->base, dev_addr, rmem->size,
>  				      DMA_MEMORY_MAP | DMA_MEMORY_EXCLUSIVE,
>  				      &mem)) {
>  		pr_err("Reserved memory: failed to init DMA memory pool at %pa, size %ld MiB\n",
> 

Robin has already commented on this - dma_pfn_offset may vary across devices
and reserved memory region may be shared between them.

Cheers
Vladimir