linux-kernel - Re: [PATCH kernel v9 17/32] powerpc/powernv: Implement accessor to TCE entry

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Message-ID: <20150429040436.GN32589@voom.redhat.com>
Date:	Wed, 29 Apr 2015 14:04:36 +1000
From:	David Gibson <david@...son.dropbear.id.au>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	linuxppc-dev@...ts.ozlabs.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH kernel v9 17/32] powerpc/powernv: Implement accessor to
 TCE entry

On Sat, Apr 25, 2015 at 10:14:41PM +1000, Alexey Kardashevskiy wrote:
> This replaces direct accesses to TCE table with a helper which
> returns an TCE entry address. This does not make difference now but will
> when multi-level TCE tables get introduces.
> 
> No change in behavior is expected.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>

Reviewed-by: David Gibson <david@...son.dropbear.id.au>


> ---
> Changes:
> v9:
> * new patch in the series to separate this mechanical change from
> functional changes; this is not right before
> "powerpc/powernv: Implement multilevel TCE tables" but here in order
> to let the next patch - "powerpc/iommu/powernv: Release replaced TCE" -
> use pnv_tce() and avoid changing the same code twice
> ---
>  arch/powerpc/platforms/powernv/pci.c | 34 +++++++++++++++++++++-------------
>  1 file changed, 21 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/pci.c b/arch/powerpc/platforms/powernv/pci.c
> index 84b4ea4..ba75aa5 100644
> --- a/arch/powerpc/platforms/powernv/pci.c
> +++ b/arch/powerpc/platforms/powernv/pci.c
> @@ -572,38 +572,46 @@ struct pci_ops pnv_pci_ops = {
>  	.write = pnv_pci_write_config,
>  };
>  
> +static __be64 *pnv_tce(struct iommu_table *tbl, long idx)
> +{
> +	__be64 *tmp = ((__be64 *)tbl->it_base);
> +
> +	return tmp + idx;
> +}
> +
>  int pnv_tce_build(struct iommu_table *tbl, long index, long npages,
>  		unsigned long uaddr, enum dma_data_direction direction,
>  		struct dma_attrs *attrs)
>  {
>  	u64 proto_tce = iommu_direction_to_tce_perm(direction);
> -	__be64 *tcep;
> -	u64 rpn;
> +	u64 rpn = __pa(uaddr) >> tbl->it_page_shift;

I guess this was a problem in the existing code, not this patch.  But
"uaddr" is a really bad name (and unsigned long is a bad type) for
what must actually be a kernel linear mapping address.

> +	long i;
>  
> -	tcep = ((__be64 *)tbl->it_base) + index - tbl->it_offset;
> -	rpn = __pa(uaddr) >> tbl->it_page_shift;
> -
> -	while (npages--)
> -		*(tcep++) = cpu_to_be64(proto_tce |
> -				(rpn++ << tbl->it_page_shift));
> +	for (i = 0; i < npages; i++) {
> +		unsigned long newtce = proto_tce |
> +			((rpn + i) << tbl->it_page_shift);
> +		unsigned long idx = index - tbl->it_offset + i;
>  
> +		*(pnv_tce(tbl, idx)) = cpu_to_be64(newtce);
> +	}
>  
>  	return 0;
>  }
>  
>  void pnv_tce_free(struct iommu_table *tbl, long index, long npages)
>  {
> -	__be64 *tcep;
> +	long i;
>  
> -	tcep = ((__be64 *)tbl->it_base) + index - tbl->it_offset;
> +	for (i = 0; i < npages; i++) {
> +		unsigned long idx = index - tbl->it_offset + i;
>  
> -	while (npages--)
> -		*(tcep++) = cpu_to_be64(0);
> +		*(pnv_tce(tbl, idx)) = cpu_to_be64(0);
> +	}
>  }
>  
>  unsigned long pnv_tce_get(struct iommu_table *tbl, long index)
>  {
> -	return ((u64 *)tbl->it_base)[index - tbl->it_offset];
> +	return *(pnv_tce(tbl, index - tbl->it_offset));
>  }
>  
>  void pnv_pci_setup_iommu_table(struct iommu_table *tbl,

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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