Re: [Qemu-devel] [PATCH v2 1/3] lsi53c895a: hide 53c895a registers in 53c810

[Mark Cave-Ayland]

On 06/05/2019 09:42, Artyom Tarasenko wrote:

> On Sun, May 5, 2019 at 12:43 PM Mark Cave-Ayland
> <address@hidden> wrote:
>>
>> On 04/05/2019 22:02, Artyom Tarasenko wrote:
>>
>>> AIX/PReP does access to the aliased IO registers of 53810.
>>> Implement aliasing to make the AIX driver work.
>>>
>>> Signed-off-by: Artyom Tarasenko <address@hidden>
>>> ---
>>>  hw/scsi/lsi53c895a.c | 17 ++++++++++++++---
>>>  1 file changed, 14 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
>>> index da7239d..6b95699 100644
>>> --- a/hw/scsi/lsi53c895a.c
>>> +++ b/hw/scsi/lsi53c895a.c
>>> @@ -2271,6 +2271,9 @@ static void lsi_scsi_realize(PCIDevice *dev, Error 
>>> **errp)
>>>      LSIState *s = LSI53C895A(dev);
>>>      DeviceState *d = DEVICE(dev);
>>>      uint8_t *pci_conf;
>>> +    uint64_t mmio_size;
>>> +    MemoryRegion *mr;
>>> +    uint16_t type = PCI_DEVICE_GET_CLASS(dev)->device_id;
>>>
>>>      pci_conf = dev->config;
>>>
>>> @@ -2279,13 +2282,21 @@ static void lsi_scsi_realize(PCIDevice *dev, Error 
>>> **errp)
>>>      /* Interrupt pin A */
>>>      pci_conf[PCI_INTERRUPT_PIN] = 0x01;
>>>
>>> -    memory_region_init_io(&s->mmio_io, OBJECT(s), &lsi_mmio_ops, s,
>>> -                          "lsi-mmio", 0x400);
>>>      memory_region_init_io(&s->ram_io, OBJECT(s), &lsi_ram_ops, s,
>>>                            "lsi-ram", 0x2000);
>>>      memory_region_init_io(&s->io_io, OBJECT(s), &lsi_io_ops, s,
>>>                            "lsi-io", 256);
>>> -
>>> +    if (type == PCI_DEVICE_ID_LSI_53C895A) {
>>> +        mmio_size = 0x400;
>>> +    } else {
>>> +        mr = g_new(MemoryRegion, 1);
>>
>> In general these days it's worth keeping the reference to the MemoryRegion 
>> within
>> LSIState since then its lifecycle is more clearly defined.
> 
> On the other hand, it's a PCI card, and can not be
> hot-plugged/removed, so the lifecycle is pretty simple here.
> Or am I missing something?

Well Thomas has been working on a set of tests that for each machine will plug 
and
unplug each device via the monitor to make sure that init/realize/unrealize work
correctly so it would be good to ensure that these tests don't leak.

However...

>>> +        memory_region_init_alias(mr, OBJECT(d), "lsi-io-alias", &s->io_io,
>>> +                                 0, 0x80);
>>> +        memory_region_add_subregion_overlap(&s->io_io, 0x80, mr, -1);
>>> +        mmio_size = 0x80;
>>
>> This feels a little strange - is it possible to see from the datasheets that 
>> the
>> 53C895A has 0x400 bytes MMIO whilst the 53C810 has 0x80 bytes MMIO? It's not 
>> clear to
>> me where the aliasing is happening.
> 
> These values are empiric. For 810 it can not be more than 0x80,
> because the AIX does access the registers with the shift of 0x80.
> For  895A we did already have 0x400.

After a bit of searching I managed to locate an 810 datasheet and in Chapter 5 
it
clearly describes the IO space (s->io_io) as being 256 bytes in size which is 
the
same as the 895A, but with 0x80-0xff aliased onto 0x00 - 0x7f.

It feels to me that rather than complicate things with an additional alias
MemoryRegion, the simplest solution would be to simply change the mask in
lsi_io_read() and lsi_io_write() to be 0x7f rather than 0xff if we've 
instantiated a
810 rather than an 895A.


ATB,

Mark.