linux-kernel - Re: [PATCH v2 10/11] xen/arm: introduce phys/dma translations in xen_dma_sync_for

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Message-ID: <20200608071221.GF15742@infradead.org>
Date:   Mon, 8 Jun 2020 00:12:21 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     jgross@...e.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, tamas@...engyel.com,
        roman@...eda.com,
        Stefano Stabellini <stefano.stabellini@...inx.com>
Subject: Re: [PATCH v2 10/11] xen/arm: introduce phys/dma translations in
 xen_dma_sync_for_*

On Wed, Jun 03, 2020 at 03:22:46PM -0700, Stefano Stabellini wrote:
> From: Stefano Stabellini <stefano.stabellini@...inx.com>
> 
> xen_dma_sync_for_cpu, xen_dma_sync_for_device, xen_arch_need_swiotlb are
> getting called passing dma addresses. On some platforms dma addresses
> could be different from physical addresses. Before doing any operations
> on these addresses we need to convert them back to physical addresses
> using dma_to_phys.
> 
> Add dma_to_phys calls to xen_dma_sync_for_cpu, xen_dma_sync_for_device,
> and xen_arch_need_swiotlb.
> 
> dma_cache_maint is fixed by the next patch.

The calling conventions because really weird now because
xen_dma_sync_for_{device,cpu} already get both a phys_addr_t and
a dma_addr_t.  

> 
> -	if (pfn_valid(PFN_DOWN(handle)))
> +	if (pfn_valid(PFN_DOWN(dma_to_phys(dev, handle))))

But here we translate the dma address to a phys addr

>  		arch_sync_dma_for_cpu(paddr, size, dir);

While this still uses the passed in paddr.  I think the uses of
addresses in this code really needs a major rethink.