Re: [PATCH kernel v2] powerpc/ioda: Set "read" permission when "write" is set

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2016-02-17 at 18:26 +1100, Alexey Kardashevskiy wrote:
> Quite often drivers set only "write" permission assuming that this
> includes "read" permission as well and this works on plenty
> platforms.
> However IODA2 is strict about this and produces an EEH when "read"
> permission is not and reading happens.
> 
> This adds a workaround in IODA code to always add the "read" bit when
> the "write" bit is set.
> 
> This fixes breakage introduced in
> 10b35b2b74 powerpc/powernv: Do not set "read" flag if
> direction==DMA_NONE
> 
> Cc: stable@vger.kernel.org # 4.2+

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> Tested-by: Douglas Miller <dougmill@linux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/powernv/pci.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/powernv/pci.c
> b/arch/powerpc/platforms/powernv/pci.c
> index 2f55c86..6a97ba4 100644
> --- a/arch/powerpc/platforms/powernv/pci.c
> +++ b/arch/powerpc/platforms/powernv/pci.c
> @@ -599,6 +599,9 @@ int pnv_tce_build(struct iommu_table *tbl, long
> index, long npages,
>  	u64 rpn = __pa(uaddr) >> tbl->it_page_shift;
>  	long i;
>  
> +	if (proto_tce & TCE_PCI_WRITE)
> +		proto_tce |= TCE_PCI_READ;
> +
>  	for (i = 0; i < npages; i++) {
>  		unsigned long newtce = proto_tce |
>  			((rpn + i) << tbl->it_page_shift);
> @@ -620,6 +623,9 @@ int pnv_tce_xchg(struct iommu_table *tbl, long
> index,
>  
>  	BUG_ON(*hpa & ~IOMMU_PAGE_MASK(tbl));
>  
> +	if (newtce & TCE_PCI_WRITE)
> +		newtce |= TCE_PCI_READ;
> +
>  	oldtce = xchg(pnv_tce(tbl, idx), cpu_to_be64(newtce));
>  	*hpa = be64_to_cpu(oldtce) & ~(TCE_PCI_READ |
> TCE_PCI_WRITE);
>  	*direction = iommu_tce_direction(oldtce);