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Date: Sun, 6 Jun 2021 11:52:33 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Sven Peter <sven@...npeter.dev>
Cc: linux-usb@...r.kernel.org, Felipe Balbi <balbi@...nel.org>,
linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] usb: dwc3: support 64 bit DMA in platform driver
On Sun, Jun 06, 2021 at 11:36:29AM +0200, Sven Peter wrote:
> Currently, the dwc3 platform driver does not explicitly ask for
> a DMA mask. This makes it fall back to the default 32-bit mask which
> breaks the driver on systems that only have RAM starting above the
> first 4G like the Apple M1 SoC.
>
> Fix this by using the same logic already present in xhci-plat.c:
> First, try to set a coherent dma mask for 64-bit, and then attempt
> again with a 32-bit mask if this fails.
>
> Signed-off-by: Sven Peter <sven@...npeter.dev>
> ---
>
> I have taken the code directly from the xhci-plat.c driver so
> I think this change should be fairly low risk.
> Unfortunately I only have the Apple M1 to test this on but here
> the driver still works with the iommu enabled which limits the
> address space to 32 bit. It also enables to use this with the iommu
> in bypass mode which requires 64 bit addresses.
>
> I believe this has been working fine so far since the dwc3 driver
> only uses a few very small buffers in host mode which might still
> fit within the first 4G of address space on many devices. The
> majority of DMA buffers are allocated inside the xhci driver which
> will already call dma_set_mask_and_coherent.
>
> Best,
>
> Sven
>
> 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 b6e53d8212cd..ef6bb6aaffd8 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 (WARN_ON(!dwc->sysdev->dma_mask))
This will cause systems to reboot if they have panic-on-warn set. Are
you sure you want that to happen?
I know you copied this from xhci-plat, but let's not duplicate bugs
please :)
thnaks,
greg k-h
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