Re: [Qemu-devel] [PATCH 05/14] eepro100: Use PCI DMA stub functions

[David Gibson]

On Wed, Nov 02, 2011 at 09:16:34AM +0200, Michael S. Tsirkin wrote:
> On Mon, Oct 31, 2011 at 05:06:49PM +1100, David Gibson wrote:
> > From: Eduard - Gabriel Munteanu <address@hidden>
[snip]
> > @@ -744,21 +713,26 @@ static void dump_statistics(EEPRO100State * s)
> >       * values which really matter.
> >       * Number of data should check configuration!!!
> >       */
> > -    cpu_physical_memory_write(s->statsaddr, &s->statistics, s->stats_size);
> > -    e100_stl_le_phys(s->statsaddr + 0, s->statistics.tx_good_frames);
> > -    e100_stl_le_phys(s->statsaddr + 36, s->statistics.rx_good_frames);
> > -    e100_stl_le_phys(s->statsaddr + 48, s->statistics.rx_resource_errors);
> > -    e100_stl_le_phys(s->statsaddr + 60, 
> > s->statistics.rx_short_frame_errors);
> > +    pci_dma_write(&s->dev, s->statsaddr,
> > +                  (uint8_t *) &s->statistics, s->stats_size);
> > +    stl_le_pci_dma(&s->dev, s->statsaddr + 0,
> > +                   s->statistics.tx_good_frames);
> > +    stl_le_pci_dma(&s->dev, s->statsaddr + 36,
> > +                   s->statistics.rx_good_frames);
> > +    stl_le_pci_dma(&s->dev, s->statsaddr + 48,
> > +                   s->statistics.rx_resource_errors);
> > +    stl_le_pci_dma(&s->dev, s->statsaddr + 60,
> > +                   s->statistics.rx_short_frame_errors);
> 
> This might introduce a bug: stlXX APIs assume aligned addresses,
> an address in statsaddr is user-controlled so I'm not sure
> it's always aligned.
> 
> Why isn't the patch simply replacing cpu_physical_memory_read
> with pci_XXX ? Any cleanups should be done separately.

Because it seemed like a good idea at the time.  When I first wrote
this, the possibility of unaligned addresses wasn't obvious to me.
So, I'm working on fixing this now.  I can take one of two approaches:

 - Simply revert this part of the change, reinstate the e100_stl
functions as calling into dma_write().

 - Alter the stX_dma() functions to work for unaligned addresses (by
falling back to dma_rw() in that case).  This is a little more
involved but might make device writing safer in future.

Anthony, Michael, any preferred direction here?

-- 
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