linux-kernel - [PATCH v3] usb: dwc3: support 64 bit DMA in platform driver

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Message-Id: <20210607061751.89752-1-sven@svenpeter.dev>
Date:   Mon,  7 Jun 2021 08:17:51 +0200
From:   Sven Peter <sven@...npeter.dev>
To:     linux-usb@...r.kernel.org
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Sven Peter <sven@...npeter.dev>
Subject: [PATCH v3] usb: dwc3: support 64 bit DMA in platform driver

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 calling dma_set_mask_and_coherent with a 64bit mask.

Signed-off-by: Sven Peter <sven@...npeter.dev>
---

Third time's a charm I hope - this time much simpler :)

I still 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

changes from v2:
 - remove both dma_coerce_mask_and_coherent and the 32 bit
   dma_set_mask_and_coherent as pointed out by Arnd Bergmann
changes from v1:
 - removed WARN_ON around !dwc->sysdev->dma_mask; pointed out by greg k-h

 drivers/usb/dwc3/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index b6e53d8212cd..ba4792b6a98f 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -1545,6 +1545,10 @@ static int dwc3_probe(struct platform_device *pdev)

 	dwc3_get_properties(dwc);

+	ret = dma_set_mask_and_coherent(dwc->sysdev, DMA_BIT_MASK(64));
+	if (ret)
+		return ret;
+
 	dwc->reset = devm_reset_control_array_get_optional_shared(dev);
 	if (IS_ERR(dwc->reset))
 		return PTR_ERR(dwc->reset);
-- 
2.25.1