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

[BALATON Zoltan]

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.
>
> Is this document here accurate as to how it works on real hardware? 
> https://intuitionbase.com/hints.php.

That should be about right. On QEMU the U-boot env vars won't work because 
NVRAM is not emulated yet so they can't be saved but you can call idetool 
from startup-sequence boot script instead for same effect (UDMA is enabled 
a bit later with that but after that it's the same).

> I can't understand why the base OS is attempting any access to BAR 4 if BMDMA 
> isn't enabled by default on real hardware due to hardware bugs.

Real hardware had problems with DMA (the VIA chip was also infamous for it 
on PC hardware and later also the ArticiaS was found to have its own 
problems) so the default is to use IDE in PIO mode and UDMA has to be 
enabled manually. But if it works (and it should on QEMU) it's much 
faster so we want to enable it.

> Are we sure 
> that the idetool hacks given in the link above to enable BMDMA haven't 
> already been run on the AmigaOS install when testing an earlier version of 
> the patches?

It was tested with my original series and works with that as my patch sets 
the default vaules for BARs and the driver reads it correctly. Then we 
tested your series too and I've noted for v2 already that it misses the 
degault value for BAR4. Other BARs don't matter as it will apparently use 
ISA IDE ports when it gets 0 or it knows that in legacy mode these shoud 
be the port values but seems to read BAR4 for UDMA and only works if the 
right default value is there, otherwise it lists DMA BAR 0 on start.

> Finally is there a bootable AmigaOS demo ISO somewhere that can be used for 
> testing?

Unfortunately AmigaOS4 is only available commercially, no free demo is 
avaialable.

Regards,
BALATON Zoltan