[U-Boot] [PATCH v2 5/7] usb: dwc2-otg: fix warnings for ep->dma_buf for LP64 builds

[Marek Vasut]

On 06/07/2017 09:49 AM, Dr. Philipp Tomsich wrote:
>> On 07 Jun 2017, at 08:28, Marek Vasut <marex at denx.de
>> <mailto:marex at denx.de>> wrote:
>>
>> On 06/06/2017 05:11 PM, Dr. Philipp Tomsich wrote:
>>>
>>>> On 06 Jun 2017, at 16:35, Marek Vasut <marex at denx.de
>>>> <mailto:marex at denx.de>> wrote:
>>>>
>>>> On 06/06/2017 03:42 PM, Philipp Tomsich wrote:
>>>>> For LP64 build w/ GCC 6.3, the handling of the ep->dma_buf variable
>>>>> when (truncating and) writing into the controller's registers is
>>>>> unsafe and triggers the following compiler warning (thus failing by
>>>>> buildman tests):
>>>>> ../drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c: In function 'setdma_rx':
>>>>> ../drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c:116:9: warning: cast
>>>>> from pointer to integer of different size [-Wpointer-to-int-cast]
>>>>>   writel((unsigned int) ep->dma_buf, &reg->out_endp[ep_num].doepdma);
>>>>>          ^
>>>>>
>>>>> This change fixes the warning and makes the code a bit more robust by
>>>>> doing the following:
>>>>> - we check whether ep->dma_buf can be safely truncated to 32 bits
>>>>> (i.e. whether dma_buf is the same value when masked to 32 bits) and
>>>>> emit an error message if that is not the case
>>>>> - we cast to a uintptr_t and let the writel macro truncate the
>>>>> uintptr_t (potentially a 64bit value) to 32bits
>>>>>
>>>>> Signed-off-by: Philipp Tomsich
>>>>> <philipp.tomsich at theobroma-systems.com
>>>>> <mailto:philipp.tomsich at theobroma-systems.com>>
>>>>>
>>>>> ---
>>>>>
>>>>> Changes in v2:
>>>>> - (new patch) fix warnings and add some robustness for the truncation
>>>>> of ep->dma_buf in dwc2-otg for LP64 builds to fix a buildman failure
>>>>> for u-boot-rockchip/master at 2b19b2f
>>>>>
>>>>> drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c | 6 +++++-
>>>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>> b/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>> index 0d6d2fb..f5c926c 100644
>>>>> --- a/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>> +++ b/drivers/usb/gadget/dwc2_udc_otg_xfer_dma.c
>>>>> @@ -113,7 +113,11 @@ static int setdma_rx(struct dwc2_ep *ep,
>>>>> struct dwc2_request *req)
>>>>> invalidate_dcache_range((unsigned long) ep->dma_buf,
>>>>> (unsigned long) ep->dma_buf + ep->len);
>>>>>
>>>>> -writel((unsigned int) ep->dma_buf, &reg->out_endp[ep_num].doepdma);
>>>>> +/* ensure that ep->dma_buf fits into 32 bits */
>>>>> +if (((uintptr_t)ep->dma_buf & 0xffffffff) != (uintptr_t)ep->dma_buf)
>>>>> +error("ep->dma_buf does not fit into a 32 bits");
>>>>
>>>> You print an error, but still continue with the function ? That'll
>>>> probably lead to a crash, you should rather abort. In fact, I suspect
>>>> you can use bounce-buffer to assure the dma buffer is in 32bit space.
>>>
>>> This tries to stay close to the current behaviour (we have no
>>> hardware to test this,
>>> but I wanted to get it out of the way as it caused buildman-failures)
>>> and to provide
>>> diagnostics for whoever first encounters an issue here.
>>>
>>> Note that I would only expect a DMA error, if someone really hit this
>>> issue ...
>>
>> So this patch is just some hypothetical fix ? What triggered creation of
>> this patch ?
> 
> Running buildman (w/ a GCC 6.3 configured as aarch-unknown-elf) against
> unrelated
> patch-series (for a Rockchip device that has a different USB controller)
> fails due to the
> warnings raised from this. Just casting those warnings away (without
> having an
> “assertion-like” diagnostic printed) doesn’t sound like the best plan
> either, though. 
> 
> Details of the buildman-failure are in the above commit-message.

Ah, hm. In that case, you should really implement the bounce buffer here
I think. Letting the transfer continue will lead to really weird
failures and/or memory corruption.

-- 
Best regards,
Marek Vasut