linux-kernel - Re: [PATCH v2] usb: dwc3: support 64 bit DMA in platform driver

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Date:   Sun, 6 Jun 2021 17:43:39 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sven Peter <sven@...npeter.dev>
Cc:     USB list <linux-usb@...r.kernel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: support 64 bit DMA in platform driver

On Sun, Jun 6, 2021 at 12:36 PM Sven Peter <sven@...npeter.dev> wrote:
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index b6e53d8212cd..4930541a8984 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -1545,6 +1545,21 @@ static int dwc3_probe(struct platform_device *pdev)
>
>         dwc3_get_properties(dwc);
>
> +       /* Try to set 64-bit DMA first */
> +       if (!dwc->sysdev->dma_mask)
> +               /* Platform did not initialize dma_mask */
> +               ret = dma_coerce_mask_and_coherent(dwc->sysdev,
> +                                                  DMA_BIT_MASK(64));
> +       else
> +               ret = dma_set_mask_and_coherent(dwc->sysdev, DMA_BIT_MASK(64));
> +
> +       /* If seting 64-bit DMA mask fails, fall back to 32-bit DMA mask */
> +       if (ret) {
> +               ret = dma_set_mask_and_coherent(dwc->sysdev, DMA_BIT_MASK(32));
> +               if (ret)
> +                       return ret;
> +       }

Please drop the dma_coerce_mask_and_coherent() code path as well: if
the device is marked as non-DMA capable in the platform, it's better have
it not be usable at all than to assume a particular bus property that may
or may not be present on that bus.

The 32-bit mask is the default on all buses you might see a dwc3 controller
on, so you can drop that as well, and just leave the
dma_set_mask_and_coherent().

        Arnd