On Thu, Jul 07, 2022 at 10:53:57AM -0700, Peter Delevoryas wrote:
On Thu, Jul 07, 2022 at 10:56:02AM +0200, Cédric Le Goater wrote:
On 7/7/22 09:17, Peter Delevoryas wrote:
It seems that aspeed_gpio_update is allowing the value for input pins to be
modified through register writes and QOM property modification.
The QOM property modification is fine, but modifying the value through
register writes from the guest OS seems wrong if the pin's direction is set
to input.
The datasheet specifies that "0" bits in the direction register select input
mode, and "1" selects output mode.
OpenBMC userspace code is accidentally writing 0's to the GPIO data
registers somewhere (or perhaps the driver is doing it through a reset or
something), and this is overwriting GPIO FRU information (board ID, slot
presence pins) that is initialized in Aspeed machine reset code (see
fby35_reset() in hw/arm/aspeed.c).
It might be good to log a GUEST_ERROR in that case, when writing to an
input GPIO and when reading from an output GPIO.
Good idea, I'll include a GUEST_ERROR for writing to an input GPIO.
I'm actually not totally certain about emitting an error when reading from an
output GPIO, because the driver can only do 8-bit reads at the finest
granularity, and if 1 of the 8 pins' direction is output, then it will be
reading the value of an output pin. But, that's not really bad, because
presumably the value will be ignored. Maybe I can go test this out on
hardware and figure out what happens though.
Did a small experiment, I was looking at some of the most significant
bits:
root@dhcp-100-96-192-133:~# devmem 0x1e780000
0x3CFF303E
root@dhcp-100-96-192-133:~# devmem 0x1e780004
0x2800000C
root@dhcp-100-96-192-133:~# devmem 0x1e780000 32 0xffffffff
root@dhcp-100-96-192-133:~# devmem 0x1e780004
0x2800000C
root@dhcp-100-96-192-133:~# devmem 0x1e780000
0x3CFF303E
root@dhcp-100-96-192-133:~# devmem 0x1e780000
0x3CFF303E
root@dhcp-100-96-192-133:~# devmem 0x1e780000 32 0
root@dhcp-100-96-192-133:~# devmem 0x1e780000
0x14FF303A
Seems like the output pin 0x20000000 was initially high, and the input
pin right next to it 0x10000000 was also high. After writing 0 to the
data register, the value in the data register changed for the output
pin, but not the input pin. Which matches what we're planning on doing
in the controller.
So yeah, I'll add GUEST_ERROR for writes to input pins but not output
pins. The driver should probably be doing a read-modify-update.
Although...if it's not, that technically wouldn't matter, behavior
wise...maybe GUEST_ERROR isn't appropriate for writes to input pins
either, for the same reason as I mentioned with reads of output pins.
I'll let you guys comment on what you think we should do.