Re: [PATCH v2 12/12] hw/isa/vt82c686: Implement relocation and toggling of SuperI/O functions

[Bernhard Beschow]

Am 24. Dezember 2023 00:51:53 UTC schrieb BALATON Zoltan <balaton@eik.bme.hu>:
>On Tue, 19 Dec 2023, Bernhard Beschow wrote:
>> Am 19. Dezember 2023 00:26:15 UTC schrieb BALATON Zoltan 
>> <balaton@eik.bme.hu>:
>>> On Mon, 18 Dec 2023, Bernhard Beschow wrote:
>>>> The VIA south bridges are able to relocate and toggle (enable or disable) 
>>>> their
>>>> SuperI/O functions. So far this is hardcoded such that all functions are 
>>>> always
>>>> enabled and are located at fixed addresses.
>>>> 
>>>> Some PC BIOSes seem to probe for I/O occupancy before activating such a 
>>>> function
>>>> and issue an error in case of a conflict. Since the functions are enabled 
>>>> on
>>>> reset, conflicts are always detected. Prevent that by implementing 
>>>> relocation
>>>> and toggling of the SuperI/O functions.
>>>> 
>>>> Note that all SuperI/O functions are now deactivated upon reset (except for
>>>> VT82C686B's serial ports where Fuloong 2e's rescue-yl seems to expect them 
>>>> to be
>>>> enabled by default). Rely on firmware -- or in case of pegasos2 on board 
>>>> code if
>>>> no -bios is given -- to configure the functions accordingly.
>>> 
>>> Pegasos2 emulates firmware when no -bios is given, this was explained in 
>>> previos commit so maybe not needed to be explained it here again so you 
>>> could drop the comment between -- -- but I don't mind.
>>> 
>>>> Signed-off-by: Bernhard Beschow <shentey@gmail.com>
>>>> ---
>>>> hw/isa/vt82c686.c | 121 ++++++++++++++++++++++++++++++++++------------
>>>> 1 file changed, 90 insertions(+), 31 deletions(-)
>>>> 
>>>> diff --git a/hw/isa/vt82c686.c b/hw/isa/vt82c686.c
>>>> index 9c2333a277..be202d23cf 100644
>>>> --- a/hw/isa/vt82c686.c
>>>> +++ b/hw/isa/vt82c686.c
>>>> @@ -15,6 +15,9 @@
>>>> 
>>>> #include "qemu/osdep.h"
>>>> #include "hw/isa/vt82c686.h"
>>>> +#include "hw/block/fdc.h"
>>>> +#include "hw/char/parallel-isa.h"
>>>> +#include "hw/char/serial.h"
>>>> #include "hw/pci/pci.h"
>>>> #include "hw/qdev-properties.h"
>>>> #include "hw/ide/pci.h"
>>>> @@ -343,6 +346,35 @@ static const TypeInfo via_superio_info = {
>>>> 
>>>> #define TYPE_VT82C686B_SUPERIO "vt82c686b-superio"
>>>> 
>>>> +static void vt82c686b_superio_update(ViaSuperIOState *s)
>>>> +{
>>>> +    isa_parallel_set_enabled(s->superio.parallel[0],
>>>> +                             (s->regs[0xe2] & 0x3) != 3);
>>>> +    isa_serial_set_enabled(s->superio.serial[0], s->regs[0xe2] & BIT(2));
>>>> +    isa_serial_set_enabled(s->superio.serial[1], s->regs[0xe2] & BIT(3));
>>>> +    isa_fdc_set_enabled(s->superio.floppy, s->regs[0xe2] & BIT(4));
>>>> +
>>>> +    isa_fdc_set_iobase(s->superio.floppy, (s->regs[0xe3] & 0xfc) << 2);
>>>> +    isa_parallel_set_iobase(s->superio.parallel[0], s->regs[0xe6] << 2);
>>>> +    isa_serial_set_iobase(s->superio.serial[0], (s->regs[0xe7] & 0xfe) << 
>>>> 2);
>>>> +    isa_serial_set_iobase(s->superio.serial[1], (s->regs[0xe8] & 0xfe) << 
>>>> 2);
>>>> +}
>>> 
>>> I wonder if some code duplication could be saved by adding a shared 
>>> via_superio_update() for this further up in the abstract via-superio class 
>>> instead of this method and vt8231_superio_update() below. This common 
>>> method in abstract class would need to handle the differences which seem to 
>>> be reg addresses offset by 0x10 and VT8231 having only 1 serial port. These 
>>> could either be handled by adding function parameters or fields to 
>>> ViaSuperIOState for this that the subclasses can set and the method check. 
>>> (Such as reg base=0xe2 for vt82c686 and 0xf2 for vt8231 and num_serial or 
>>> similar for how many ports are there then can have a for loop for those 
>>> that would only run once for vt8231).
>> 
>> Only the enable bits and the parallel port base address line up, the serial 
>> port(s) and the floppy would need special treatment. Not worth it IMO.
>
>Missed this part in previous reply. The serial ports would be taken care of by 
>a loop for number of ports so only the floppy needs an if which could also use 
>the number of serial ports for lack of better way to distinguish these cips 
>easily. Number of ports are in the superio class which you could get with 
>ISA_SUPERIO_GET_CLASS (see via_superio_realize) then serial.count would be 2 
>for 686b and 1 for 8231.

I'm not very convinced about telling the device models apart by their number of 
sub devices. So let's omit this part for now.

>
>But now I think another way may be better that is to drop the superio_update 
>function as this updates all functions on writing any register unnecessarily 
>and put the lines from it in the vt*_superio_cfg_write() functions under the 
>separate cases. This was the original intent, that's why the reset function 
>goes through that write function so it can enable/disable functions. That way 
>you could apply mask on write so via_superio_cfg_read() would return 0 bits as 
>0 (although the data sheet is not clear about what real chip does, just says 
>these must be 0 not that it's enforced but if we enforce that it's probably 
>better to return the effective value on read as well). Then when state saving 
>is added in separate patch you can have a similar function as 
>vt82c686b_superio_reset() (or rename that to update and make it use regs[xx] 
>instead of constant values and call that from reset after setting regs values 
>like you did here. But that needs more thought as the vmstate added by this 
>patch is incomplete and would not work so you could just drop it for now and 
>add it later with also adding other necessary state as well. The idea was to 
>implement the chip first then add state saving so we don't need to bother with 
>breaking it until we have a good enough implementation. So far the state 
>saving there is just left over from the old model which never worked and only 
>left there for reminder but only wanted to fix once the model is complete 
>enough.

Indeed, the patch obviously does too much if it misses details in vmstate. 
Let's omit vmstate handling for now and go with your suggestion.

Any other comments from your side before the next iteration?

>
>So I think for now you could drop vmstate stuff and distribute the 
>superio_update lines in the superio_cfg_write functions so each reg only 
>controls the function it should control. Then when vmstate saving is added 
>later it could reuse superio_reset as an update function adding a new reset 
>func setting reg values and calling the old reset/new update function. Does 
>that make sense?

What I don't like about the vt*_superio_cfg_write() being called during reset 
is the trace logs they produce. They are hard to tell apart from guests poking 
these registers, especially during reboot. So I wonder if this could be 
addressed when implementing vmstate handling as you suggest. Not too big of a 
deal, though.

Best regards,
Bernhard

>
>Regards,
>BALATON Zoltan