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Re: [PATCH] mtd: sh_flctl: pass FIFO as physical address

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  Re: [PATCH] mtd: sh_flctl: pass FIFO as physical address Brian Norris <computersforpeace@gmail.com> - 2015-12-19 03:30 +0100

#1295267 — Re: [PATCH] mtd: sh_flctl: pass FIFO as physical address

On Tue, Dec 08, 2015 at 04:38:12PM +0100, Arnd Bergmann wrote:
> By convention, the FIFO address we pass using dmaengine_slave_config
> is a physical address in the form that is understood by the DMA
> engine, as a dma_addr_t, phys_addr_t or resource_size_t.
> 
> The sh_flctl driver however passes a virtual __iomem address that
> gets cast to dma_addr_t in the slave driver. This happens to work
> on shmobile because that platform sets up an identity mapping for
> its MMIO regions, but such code is not portable to other platforms,
> and prevents us from ever changing the platform mapping or reusing
> the driver on other architectures like ARM64 that might not have the
> mapping.
> 
> We also get a warning about a type mismatch for the case that
> dma_addr_t is wider than a pointer, i.e. when CONFIG_LPAE is set:
> 
> drivers/mtd/nand/sh_flctl.c: In function 'flctl_setup_dma':
> drivers/mtd/nand/sh_flctl.c:163:17: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
>   cfg.dst_addr = (dma_addr_t)FLDTFIFO(flctl);
> 
> This changes the driver to instead pass the physical address of
> the FIFO that is extracted from the MMIO resource, making the
> code more portable and avoiding the warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

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