[U-Boot] [PATCH v3 4/4] usb: dwc2: invalidate dcache before starting DMA

[Ziyuan Xu]

On 2016年07月12日 20:59, Simon Glass wrote:
> Hi Ziyuan,
>
> On 6 July 2016 at 03:34, Ziyuan Xu <xzy.xu at rock-chips.com> wrote:
>> From: Xu Ziyuan <xzy.xu at rock-chips.com>
>>
>> Invalidate dcache before starting the DMA to ensure coherency. In case
>> there are any dirty lines from the DMA buffer in the cache, subsequent
>> cache-line replacements may corrupt the buffer in memory while the DMA
>> is still going on. Cache-line replacement can happen if the CPU tries to
>> bring some other memory locations into the cache while the DMA is going
>> on.
>>
>> Signed-off-by: Ziyuan Xu <xzy.xu at rock-chips.com>
>> ---
>>
>> Changes in v3:
>> - New commit since v3 to fix the coherence issue between memory and
>> cache
>>
>> Changes in v2: None
>>
>>   drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c b/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>> index 12f5c85..0d6d2fb 100644
>> --- a/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>> +++ b/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>> @@ -110,6 +110,9 @@ static int setdma_rx(struct dwc2_ep *ep, struct dwc2_request *req)
>>
>>          ctrl =  readl(&reg->out_endp[ep_num].doepctl);
>>
>> +       invalidate_dcache_range((unsigned long) ep->dma_buf,
>> +                               (unsigned long) ep->dma_buf + ep->len);
> There is an invalidate in complete_rx() which is one of the callers
> for this function. It seems to me that we should not have this in two
> places. Why do we have this problem? Is it because the other calls to
> setdma_rx() don't invalidate?

Yup, invoke invalidate method twice during one complete transmission:
1- invalidate in setdma_rx() in case of  the write back cache, present 
from cache-line replacement after DMA transmission complete.
i.e.
1) dma_buf = "123456789abcd";
2) didn't invalidate in setdma_rx()
3) DMA complete interrupt coming
4) invalidate in complete_rx()
5) read dma_buf, it's "123456789abcd"

If invalidate in step 2, we will achieve correct data.
I think it's necessary to invalidate before starting DMA, and 
doc/README.arm-caches describe  details.
2- invalidate in complete_rx(), cpu read the dma_buf from memory directly.

> I think the invalidate should happen just before reading the data. Can
> you please check if the other invalidate is needed? Also see how it
> cache-aligns the end address.
memalign(CONFIG_SYS_CACHELINE_SIZE, EP_BUFFER_SIZE);
cache-aligns: 64 bytes.
dma_buffer size: 4096

I had check cache-aligins and end address, rightful.
Furthermore, everything works fine with noncached_alloc().
>
>> +
>>          writel((unsigned int) ep->dma_buf, &reg->out_endp[ep_num].doepdma);
>>          writel(DOEPT_SIZ_PKT_CNT(pktcnt) | DOEPT_SIZ_XFER_SIZE(length),
>>                 &reg->out_endp[ep_num].doeptsiz);
>> --
>> 1.9.1
>>
>>
> Regards,
> Simon
>
>
>