On Sat, Dec 10, 2016 at 05:36:34PM +0000, Jonathan Cameron wrote: > On 09/12/16 10:24, Marcus Folkesson wrote: > > The buffer needs to be DMA-safe when used with spi_read() > > > > Signed-off-by: Marcus Folkesson <[email protected]> > Please read the documentation in include/linux/gfp.h about GFP_DMA. > > Specifically: > 220 * GFP_DMA exists for historical reasons and should be avoided where > possible. > 221 * The flags indicates that the caller requires that the lowest zone be > 222 * used (ZONE_DMA or 16M on x86-64). Ideally, this would be removed but > 223 * it would require careful auditing as some users really require it and > 224 * others use the flag to avoid lowmem reserves in ZONE_DMA and treat > the > 225 * lowest zone as a type of emergency reserve. > > Seems unlikely this applies! This caught me by surprise as I didn't even know > that flag existed - hence I went digging. > > Jonathan
Always learn something! I did not know it was depricated, seems like the comment about GFP_DMA was commited just a year ago. I had a problem with a driver on my own that by using a non DMA-safe buffer, so I was digging around looking for similiar cases in the kernel. I thought other drivers (iio/common/ssp_sensors/sspi_spi.c, input/rmi4/rmi_spi.c) was using GFP_DMA for this purpose. Anyway, thanks. Cheers, Marcus Folkesson
