Re: [PATCH v3 0/4] ide: implement simple legacy/native mode switching for PCI IDE controllers

[Kevin Wolf]

Am 20.11.2023 um 16:02 hat BALATON Zoltan geschrieben:
> On Mon, 20 Nov 2023, Mark Cave-Ayland wrote:
> > On 20/11/2023 13:42, Kevin Wolf wrote:
> > > Am 20.11.2023 um 14:09 hat BALATON Zoltan geschrieben:
> > > > On Mon, 20 Nov 2023, Mark Cave-Ayland wrote:
> > > > > On 19/11/2023 21:43, BALATON Zoltan wrote:
> > > > > > On Thu, 16 Nov 2023, Mark Cave-Ayland wrote:
> > > > > > > This series adds a simple implementation of legacy/native mode
> > > > > > > switching for PCI
> > > > > > > IDE controllers and updates the via-ide device to use it.
> > > > > > > 
> > > > > > > The approach I take here is to add a new pci_ide_update_mode()
> > > > > > > function which handles
> > > > > > > management of the PCI BARs and legacy IDE ioports for each mode
> > > > > > > to avoid exposing
> > > > > > > details of the internal logic to individual PCI IDE controllers.
> > > > > > > 
> > > > > > > As noted in [1] this is extracted from a local WIP branch I have
> > > > > > > which contains
> > > > > > > further work in this area. However for the moment
> > > > > > > I've kept it simple (and
> > > > > > > restricted it to the via-ide device) which is good
> > > > > > > enough for Zoltan's PPC
> > > > > > > images whilst paving the way for future improvements after 8.2.
> > > > > > > 
> > > > > > > Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> > > > > > > 
> > > > > > > [1] 
> > > > > > > https://lists.gnu.org/archive/html/qemu-devel/2023-10/msg05403.html
> > > > > > > 
> > > > > > > v3:
> > > > > > > - Rebase onto master
> > > > > > > - Move ide_portio_list[] and ide_portio_list2[] to IDE core to
> > > > > > > prevent duplication in
> > > > > > >   hw/ide/pci.c
> > > > > > > - Don't zero BARs when switching from native mode to legacy
> > > > > > > mode, instead always force
> > > > > > >   them to read zero as suggested in the PCI IDE specification
> > > > > > > (note: this also appears
> > > > > > >   to fix the fuloong2e machine booting from IDE)
> > > > > > 
> > > > > > Not sure you're getting this, see also:
> > > > > > https://lists.nongnu.org/archive/html/qemu-devel/2023-11/msg04167.html
> > > > > > but this seems to break latest version of the AmigaOS driver for
> > > > > > some reason. I assume this is the BAR zeroing that causes this as it
> > > > > > works with v2 series and nothing else changed in v3 that could cause
> > > > > > this. Testing was done by Rene Engel, cc'd so maybe he can add more
> > > > > > info. It seems to work with my patch that sets BARs to legacy values
> > > > > > and with v2 that sets them to 0 but not with v3 which should also
> > > > > > read 0 but maybe something is off here.
> > > > > 
> > > > > I've been AFK for a few days, so just starting to catch up on various
> > > > > bits and pieces.
> > > > 
> > > > OK just wasn't sure if you saw my emails at all as it happened before 
> > > > that
> > > > some spam filters disliked my mail server and put messages in the spam
> > > > folder.
> > > > 
> > > > > The only difference I can think of regarding the BAR zeroing is that 
> > > > > the
> > > > > BMDMA BAR is zeroed here. Does the following diff fix things?
> > > > 
> > > > This helps, with this the latest driver does not crash but still
> > > > reads BAR4
> > > > as 0 instead of 0xcc00 so UDMA won't work but at least it boots.
> > > 
> > > And disabling only the first four BARs is actually what the spec says,
> > > too. So I'll make this change to the queued patches.
> > 
> > That was definitely something that I thought about: what should happen
> > to BARs outside of the ones mentioned in the PCI IDE controller
> > specification? It seems reasonable to me just to consider BARS 0-3 for
> > zeroing here.
> > 
> > > If I understand correctly, UDMA didn't work before this series either,
> > > so it's a separate goal and doing it in its own patch is best anyway.
> > > 
> > > As we don't seem to have a good place to set a default, maybe just
> > > overriding it in via_ide_cfg_read(), too, and making it return 0xcc01 in
> > > compatibility mode is enough?
> > 
> > It's difficult to know whether switching to legacy mode on the via-ide
> > device resets BAR4 to its default value, or whether it is simply left
> > unaltered. For 8.2 I don't mind too much as long as the logic is
> > separate from the BAR zeroing logic (which will eventually be lifted up
> > into hw/ide/pci.c).
> 
> My original patch checked for BAR being unset and only reset to defailt in
> that case so it won't clobber a value set by something (like pegasos2
> firmware) but will set default for amigaone which does not program the BAR
> just uses the default legacy mode (which is the default on real chip but we
> have to make that happen on QEMU after reset). So setting it to default if
> it's unset when switching to legacy seems like a safe bet and testing with
> my patch did not find problem with that.

How about setting the default if it's unset on the first read after
reset instead of only on switching modes? I'd like to avoid that the
guest could observe surprising state changes, even if the OSes we're
currently looking at don't do that. It just seems more robust than
introducing random magic at arbitrary points.

Kevin