Re: [Qemu-devel] [PATCH v3 16/16] [RFC] dma/rc4030: do multiple calls to address_space_rw when doing DMA transfers

[Peter Maydell]

On 10 June 2015 at 20:37, Hervé Poussineau <address@hidden> wrote:
> Hi Leon,
>
>
> Le 10/06/2015 14:00, Leon Alrae a écrit :
>>
>> Hi Hervé,
>>
>> On 03/06/2015 21:45, Hervé Poussineau wrote:
>>>
>>> This fixes Windows NT 4.0/MIPS, which was always bugchecking with
>>> IRQL_NOT_LESS_OR_EQUAL.
>>>
>>> Signed-off-by: Hervé Poussineau <address@hidden>
>>> ---
>>>   hw/dma/rc4030.c | 14 ++++++++++++--
>>>   1 file changed, 12 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/hw/dma/rc4030.c b/hw/dma/rc4030.c
>>> index 3efa6de..deac0a8 100644
>>> --- a/hw/dma/rc4030.c
>>> +++ b/hw/dma/rc4030.c
>>> @@ -681,6 +681,7 @@ static void rc4030_do_dma(void *opaque, int n,
>>> uint8_t *buf, int len, int is_wri
>>>       rc4030State *s = opaque;
>>>       hwaddr dma_addr;
>>>       int dev_to_mem;
>>> +    int i;
>>>
>>>       s->dma_regs[n][DMA_REG_ENABLE] &= ~(DMA_FLAG_TC_INTR |
>>> DMA_FLAG_MEM_INTR | DMA_FLAG_ADDR_INTR);
>>>
>>> @@ -699,8 +700,17 @@ static void rc4030_do_dma(void *opaque, int n,
>>> uint8_t *buf, int len, int is_wri
>>>       dma_addr = s->dma_regs[n][DMA_REG_ADDRESS];
>>>
>>>       /* Read/write data at right place */
>>> -    address_space_rw(&s->dma_as, dma_addr, MEMTXATTRS_UNSPECIFIED,
>>> -                     buf, len, is_write);
>>> +    for (i = 0; i < len; ) {
>>> +        int ncpy = DMA_PAGESIZE - (dma_addr & (DMA_PAGESIZE - 1));
>>> +        if (ncpy > len - i) {
>>> +            ncpy = len - i;
>>> +        }
>>> +        address_space_rw(&s->dma_as, dma_addr, MEMTXATTRS_UNSPECIFIED,
>>> +                         buf + i, ncpy, is_write);
>>> +
>>> +        dma_addr += ncpy;
>>> +        i += ncpy;
>>> +    }
>>>
>>>       s->dma_regs[n][DMA_REG_ENABLE] |= DMA_FLAG_TC_INTR;
>>>       s->dma_regs[n][DMA_REG_COUNT] -= len;
>>>
>>
>> I'm sending out current target-mips queue soon and I can include this
>> series,
>> but I'm not quite sure what to do with this RFC patch. I presume you put
>> RFC
>> here because it's a workaround for a bug, but it's not clear where the
>> actual
>> bug is?
>
>
> Indeed, that's a workaround for a bug that I failed to identify. You can
> still take the RFC patch as a patch, as I didn't see any objection (yet).
> I think we can defer the bug correction for later.

...but address_space_rw() is supposed to be the same as if
you do a bunch of shorter writes, so if we have a problem
in the memory system core we should really track it down...

Paolo, does this look familiar at all?

-- PMM