[Qemu-devel] Re: bonito: PCI_STATUS questions

[chen huacai <zltjiangshi@gmail.com>]

Yes, I think so.

On Fri, Oct 29, 2010 at 4:16 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Thu, Oct 28, 2010 at 04:31:33PM +0800, chen huacai wrote:
>> Please see bonito64_pcibios_config_access() in
>> arch/mips/pci/ops-bonito64.c of Linux kernel code.
>> You will find something useful.
>
>
> Thanks!
> I found this:
>
>        /* Clear aborts */
>        BONITO_PCICMD |= BONITO_PCICMD_MABORT_CLR | BONITO_PCICMD_MTABORT_CLR;
>
>        BONITO_PCIMAP_CFG = (addr >> 16) | type;
>
>        /* Flush Bonito register block */
>        dummy = BONITO_PCIMAP_CFG;
>        mmiowb();
>
>        addrp = CFG_SPACE_REG(addr & 0xffff);
>        if (access_type == PCI_ACCESS_WRITE) {
>                writel(cpu_to_le32(*data), addrp);
>                /* Wait till done */
>                while (BONITO_PCIMSTAT & 0xF);
>        } else {
>                *data = le32_to_cpu(readl(addrp));
>        }
>
>        /* Detect Master/Target abort */
>        if (BONITO_PCICMD & (BONITO_PCICMD_MABORT_CLR |
>                             BONITO_PCICMD_MTABORT_CLR)) {
>                /* Error occurred */
>
>                /* Clear bits */
>                BONITO_PCICMD |= (BONITO_PCICMD_MABORT_CLR |
>                                  BONITO_PCICMD_MTABORT_CLR);
>
>                return -1;
>        }
>
> So it looks like guest will clear bits, perform a transaction
> then check error bits. In other words, it looks like it
> assumes that writing 1 to these bits will clear them.
> Correct?
>
>> On Thu, Oct 28, 2010 at 12:54 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
>> > On Thu, Oct 28, 2010 at 08:57:01AM +0800, chen huacai wrote:
>> >> Because the code in PMON and Linux kernel use these bits to verify r/w
>> >> operations. If one of them is 1 after r/w, PMON and Linux will
>> >> consider r/w has failed.
>> >
>> > Where's that code in Linux?
>> >
>> >> I guess that software will not set them to 1, because it is set by
>> >> hardware when operation fails.
>> >
>> > So I guess just making these write 1 to clear according to spec will work?
>> >
>> >> On Thu, Oct 28, 2010 at 12:12 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
>> >> > I see code in bonito.c that clears bits:
>> >> > PCI_STATUS_REC_MASTER_ABORT | PCI_STATUS_REC_TARGET_ABORT
>> >> > on each read and write.
>> >> >
>> >> > However
>> >> > 1. I don't see anything in code that would set these bits
>> >> > 2. The PCI spec says this about the status register:
>> >> >
>> >> >        Reads to this register behave normally. Writes are slightly different in
>> >> >        that bits can be reset, but not set. A one bit is reset (if it is not
>> >> >        read-only) whenever the register is written, and the write data in the
>> >> >        corresponding bit location is a 1. For instance, to clear bit 14 and not
>> >> >        affect any other bits, write the value 0100_0000_0000_0000b to the
>> >> >        register.
>> >> >
>> >> > while the code in bonito.c resets the bits to 0 on each write.
>> >> >
>> >> > Comments?
>> >> >
>> >> > --
>> >> > MST
>> >> >
>> >>
>> >>
>> >>
>> >> --
>> >> Huacai Chen
>> >
>>
>>
>>
>> --
>> Huacai Chen
>



-- 
Huacai Chen