Re: [PATCH] usb: devio: fix mmap() on non-coherent DMA architectures

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Aug 01, 2019 at 03:04:36PM -0700, gavinli@thegavinli.com wrote:
> From: Gavin Li <git@thegavinli.com>
> 
> On architectures that are not (or are optionally) DMA coherent,
> dma_alloc_coherent() returns an address into the vmalloc space,
> and calling virt_to_phys() on this address returns an unusable
> physical address.
> 
> This patch replaces the raw remap_pfn_range() call with a call to
> dmap_mmap_coherent(), which takes care of the differences between
> coherent and non-coherent code paths.
> 
> Tested on an arm64 rk3399 board.
> 
> Signed-off-by: Gavin Li <git@thegavinli.com>
> ---
>  drivers/usb/core/devio.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)

Should this be backported to the stable kernel trees to fix the issue on
those platforms?  If so, how far back?  What commit caused this problem
to occur?

thanks,

greg k-h