Re: [PATCH 3/5] hw/pci-host/bonito: Allow PCI config accesses smaller than 32-bit

[BALATON Zoltan <balaton@eik.bme.hu>]

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On Thu, 24 Jun 2021, Philippe Mathieu-Daudé wrote:
> When running the official PMON firmware for the Fuloong 2E, we see
> 8-bit and 16-bit accesses to PCI config space:
>
>  $ qemu-system-mips64el -M fuloong2e -bios pmon_2e.bin \
>    -trace -trace bonito\* -trace pci_cfg\*
>
>  pci_cfg_write vt82c686b-pm 05:4 @0x90 <- 0xeee1
>  bonito_spciconf_small_access PCI config address is smaller then 32-bit, addr: 0x4d2, size: 2
>  pci_cfg_write vt82c686b-pm 05:4 @0xd2 <- 0x1
>  pci_cfg_write vt82c686b-pm 05:4 @0x4 <- 0x1
>  pci_cfg_write vt82c686b-isa 05:0 @0x4 <- 0x7
>  bonito_spciconf_small_access PCI config address is smaller then 32-bit, addr: 0x81, size: 1
>  pci_cfg_read vt82c686b-isa 05:0 @0x81 -> 0x0
>  bonito_spciconf_small_access PCI config address is smaller then 32-bit, addr: 0x81, size: 1
>  pci_cfg_write vt82c686b-isa 05:0 @0x81 <- 0x80
>  bonito_spciconf_small_access PCI config address is smaller then 32-bit, addr: 0x83, size: 1
>  pci_cfg_write vt82c686b-isa 05:0 @0x83 <- 0x89
>  bonito_spciconf_small_access PCI config address is smaller then 32-bit, addr: 0x85, size: 1
>  pci_cfg_write vt82c686b-isa 05:0 @0x85 <- 0x3
>  bonito_spciconf_small_access PCI config address is smaller then 32-bit, addr: 0x5a, size: 1
>  pci_cfg_write vt82c686b-isa 05:0 @0x5a <- 0x7
>  bonito_spciconf_small_access PCI config address is smaller then 32-bit, addr: 0x85, size: 1
>  pci_cfg_write vt82c686b-isa 05:0 @0x85 <- 0x1
>
> Also this is what the Linux kernel does since it supports the Bonito
> north bridge:
> https://elixir.bootlin.com/linux/v2.6.15/source/arch/mips/pci/ops-bonito64.c#L85
>
> So it seems safe to assume the datasheet is incomplete or outdated
> regarding the address constraints.
>
> This problem was exposed by commit 911629e6d3773a8adeab48b
> ("vt82c686: Fix SMBus IO base and configuration registers").
>
> Reported-by: BALATON Zoltan <balaton@eik.bme.hu>
> Suggested-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> hw/pci-host/bonito.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/pci-host/bonito.c b/hw/pci-host/bonito.c
> index 751fdcec689..3c10608c9a2 100644
> --- a/hw/pci-host/bonito.c
> +++ b/hw/pci-host/bonito.c
> @@ -187,7 +187,7 @@ FIELD(BONGENCFG, PCIQUEUE,      12, 1)
> #define BONITO_PCICONF_FUN_MASK        0x700    /* [10:8] */
> #define BONITO_PCICONF_FUN_OFFSET      8
> #define BONITO_PCICONF_REG_MASK_DS     (~3)         /* Per datasheet */
> -#define BONITO_PCICONF_REG_MASK        0xFC
> +#define BONITO_PCICONF_REG_MASK_HW     0xff         /* As seen on hardware */

I think we didn't really see it on hardware just inferred this from what 
the firmware does. That's a slight difference but may worth noting so 
people later don't think this was really tested with real hardware. Maybe 
"As seen with PMON"? Also if this is a loongson thing as was thought in 
the thread in December then maybe the #define could be named that instead 
of _HW so if somebody wants to reuse this model later ad Bonito then know 
that it implements the Loongson version.

Regards,
BALATON Zoltan

> #define BONITO_PCICONF_REG_OFFSET      0
>
>
> @@ -466,7 +466,7 @@ static uint32_t bonito_sbridge_pciaddr(void *opaque, hwaddr addr)
>              BONITO_PCICONF_IDSEL_OFFSET;
>     devno = ctz32(idsel);
>     funno = (cfgaddr & BONITO_PCICONF_FUN_MASK) >> BONITO_PCICONF_FUN_OFFSET;
> -    regno = (cfgaddr & BONITO_PCICONF_REG_MASK) >> BONITO_PCICONF_REG_OFFSET;
> +    regno = (cfgaddr & BONITO_PCICONF_REG_MASK_HW) >> BONITO_PCICONF_REG_OFFSET;
>
>     if (idsel == 0) {
>         error_report("error in bonito pci config address 0x" TARGET_FMT_plx
>