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Re: [Qemu-devel] [PATCH 05/14] eepro100: Use PCI DMA stub functions
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH 05/14] eepro100: Use PCI DMA stub functions |
Date: |
Fri, 4 Nov 2011 11:28:03 +1100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Nov 03, 2011 at 02:25:45PM +0200, Michael S. Tsirkin wrote:
> On Thu, Nov 03, 2011 at 04:16:34PM +1100, David Gibson wrote:
> > 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.
>
> Yes but then we lose the atomicity guarantee. So this might
> still result in subtle emulation bugs.
Sorry, I should have been clearer - I was planning to fall back to
dma_rw() *only* for unaligned addresses. Aligned addresses would
still have the atomicity guarantee.
> > Anthony, Michael, any preferred direction here?
>
> For 1.0 I'd go for option 1 as the simplest.
--
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
- Re: [Qemu-devel] [PATCH 05/14] eepro100: Use PCI DMA stub functions, (continued)
Re: [Qemu-devel] [PATCH 05/14] eepro100: Use PCI DMA stub functions, Michael S. Tsirkin, 2011/11/02
Re: [Qemu-devel] [PATCH 05/14] eepro100: Use PCI DMA stub functions, Michael S. Tsirkin, 2011/11/02