Re: [PATCH 2/2] usb: dwc3: Add driver for Xilinx platforms
From: Robin Murphy <robin.murphy@arm.com>
Date: 2020-08-27 18:46:42
Also in:
linux-devicetree, linux-usb, lkml
On 2020-08-26 19:44, Manish Narani wrote: [...]
+ /*
+ * This routes the usb dma traffic to go through CCI path instead
+ * of reaching DDR directly. This traffic routing is needed to
+ * make SMMU and CCI work with USB dma.
+ */
+ if (of_dma_is_coherent(dev->of_node) || dev->iommu_group) {
+ reg = readl(priv_data->regs + XLNX_USB_COHERENCY);
+ reg |= XLNX_USB_COHERENCY_ENABLE;
+ writel(reg, priv_data->regs + XLNX_USB_COHERENCY);
+ }This looks rather suspect - coherency should be based on coherency, not on whether an IOMMU group is present. If the device isn't described as coherent in the DT, then any SMMU mappings will end up using attributes that will downgrade traffic to be non-snooping anyway. And if the SMMU is enabled but not translating (e.g. "iommu.passthrough=1") then enabling hardware coherency when the DMA layer hasn't been told about it can potentially lead to nasty subtle problems and data loss. Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel