linux-kernel - Re: [PATCH v1 1/2] usb:dwc3: Enable support for 64-bit system

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Date:	Fri, 15 Jan 2016 21:28:47 -0600
From:	Felipe Balbi <balbi@...nel.org>
To:	"Thang Q. Nguyen" <tqnguyen@....com>
Cc:	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm@...ts.infradead.org,
	Phong Vo <pvo@....com>, Loc Ho <lho@....com>, patches@....com
Subject: Re: [PATCH v1 1/2] usb:dwc3: Enable support for 64-bit system


Hi,

"Thang Q. Nguyen" <tqnguyen@....com> writes:
> Hi Balbi,
>
> On Thu, Jan 14, 2016 at 10:47 PM, Felipe Balbi <balbi@...nel.org> wrote:
>>
>>
>> Hi,
>>
>> "Thang Q. Nguyen" <tqnguyen@....com> writes:
>> > Add 64-bit DMA operation support to the USB DWC3 driver.
>> > First attempt to set the coherent DMA mask for 64-bit DMA.
>> > If that failed, attempt again with 32-bit DMA.
>> >
>> > Signed-off-by: Thang Q. Nguyen <tqnguyen@....com>
>> > ---
>> >  drivers/usb/dwc3/core.c | 15 +++++++++++++++
>> >  1 file changed, 15 insertions(+)
>> >
>> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
>> > index 22b47973..9818d6b 100644
>> > --- a/drivers/usb/dwc3/core.c
>> > +++ b/drivers/usb/dwc3/core.c
>> > @@ -829,6 +829,21 @@ static int dwc3_probe(struct platform_device *pdev)
>> >       dwc->mem = mem;
>> >       dwc->dev = dev;
>> >
>> > +     /* Try to set 64-bit DMA first */
>> > +     if (WARN_ON(!pdev->dev.dma_mask))
>>
>> why the WARN_ON() ?
>
> In my opinion, pdev->dev.dma_mask is expected to be set correctly. And

sure is, but a WARN_ON() will print out a stack dump, which looks
scary. Besides, if it's not set you're already fixing the problem.

> the issue happen just in case of DT boot and CONFIG_DMA_CMA=n, the
> pdev->dev.dma_mask value is not set. So, I set WARN_ON there to notify

why isn't it set ?

> that we expect pdev->dev.dma_mask set but not.

why don't you fix that case, instead ?

-- 
balbi

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