Re: [PATCH 0/3] mtd: spi-nor: fix DMA-unsafe buffer issue between MTD and SPI

[Trent Piepho]

On Sun, 2017-12-24 at 05:36 +0100, Cyrille Pitchen wrote:
> this series tries to solve a long time issue of compatibility between the
> MTD and SPI sub-systems about whether we should use DMA-safe memory.

Can this should replace SoC specific fixes like:

c687c46e9e45
spi: spi-ti-qspi: Use bounce buffer if read buffer is not DMA'ble

7094576ccdc3
spi: atmel: fix corrupted data issue on SAM9 family SoCs

Or, since this only fixes instances of DMA-unsafe buffers used in
access to SPI NOR flash chips, and since there are other SPI master
interface users, those chip specific fixes in some/all spi master
drivers are still needed to fix transfers not originated via spi-nor? 
Or are all the previous fixes necessary because of spi-nor flash (via
ubifs or jffs2) and once that's fixed via this series there are no more
originators of dma-unsafe buffers?

> The SPI sub-system has already implemented a work-around on its side,
> based on the spi_map_buf() function. However this function has its own
> limitation too. Especially, even if it builds a 'struct scatterlist' from
> a vmalloc'ed buffer, calling dma_map_sg() is still not safe on all
> architectures. Especially, on ARM cores using either VIPT or VIVT data
> caches, dma_map_sg() doesn't take the cache aliases issue into account.
> Then numerous crashes were reported for such architectures.

Could the above issue also be fixed via calls to
flush_kernel_vmap_range() and invalidate_kernel_vmap_range() to keep
the data cache valid?  Or is there a reason that won't work?