Re: [PATCH v2 3/3] hw/ide/via: implement legacy/native mode switching

[Kevin Wolf <kwolf@redhat.com>]

Am 06.11.2023 um 17:13 hat BALATON Zoltan geschrieben:
> On Mon, 6 Nov 2023, Kevin Wolf wrote:
> > Am 25.10.2023 um 00:40 hat Mark Cave-Ayland geschrieben:
> > > Allow the VIA IDE controller to switch between both legacy and native modes by
> > > calling pci_ide_update_mode() to reconfigure the device whenever PCI_CLASS_PROG
> > > is updated.
> > > 
> > > This patch moves the initial setting of PCI_CLASS_PROG from via_ide_realize() to
> > > via_ide_reset(), and removes the direct setting of PCI_INTERRUPT_PIN during PCI
> > > bus reset since this is now managed by pci_ide_update_mode(). This ensures that
> > > the device configuration is always consistent with respect to the currently
> > > selected mode.
> > > 
> > > Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> > > Tested-by: BALATON Zoltan <balaton@eik.bme.hu>
> > > Tested-by: Bernhard Beschow <shentey@gmail.com>
> > 
> > As I already noted in patch 1, the interrupt handling seems to be wrong
> > here, it continues to use the ISA IRQ in via_ide_set_irq() even after
> > switching to native mode.
> 
> That's a peculiarity of this via-ide device. It always uses 14/15 legacy
> interrupts even in native mode and guests expect that so using native
> interrupts would break pegasos2 guests. This was discussed and tested
> extensively before.

This definitely needs a comment to explain the situation then because
this is in violation of the spec. If real hardware behaves like this,
it's what we should do, of course, but it's certainly unexpected and we
should explicitly document it to avoid breaking it later when someone
touches the code who doesn't know about this peculiarity.

Kevin