linux-kernel - Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

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Date:	Wed, 27 Apr 2016 14:59:00 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Felipe Balbi <balbi@...nel.org>
Cc:	Grygorii Strashko <grygorii.strashko@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	linux-usb@...r.kernel.org, Sekhar Nori <nsekhar@...com>,
	linux-kernel@...r.kernel.org,
	David Fisher <david.fisher1@...opsys.com>,
	"Thang Q. Nguyen" <tqnguyen@....com>,
	linux-arm-kernel@...ts.infradead.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent
 dev

On Wed, Apr 27, 2016 at 08:41:06AM +0300, Felipe Balbi wrote:
> Grygorii Strashko <grygorii.strashko@...com> writes:
> > On 04/26/2016 09:17 AM, Felipe Balbi wrote:
> >> Grygorii Strashko <grygorii.strashko@...com> writes:
> >>> Now not all DMA paremters configured properly for "xhci-hcd" platform
> >>> device which is created manually. For example: dma_pfn_offset, dam_ops
> >>> and iommu configuration will not corresponds "dwc3" devices
> >>> configuration. As result, this will cause problems like wrong DMA
> >>> addresses translation on platforms with LPAE enabled like Keystone 2.
> >>>
> >>> When platform is using DT boot mode the DMA configuration will be
> >>> parsed and applied from DT, so, to fix this issue, reuse
> >>> of_dma_configure() API and retrieve DMA configuartion for "xhci-hcd"
> >>> from DWC3 device node.
> >> 
> >> patch is incomplete. You left out non-DT users which might suffer from
> >> the same problem.
> >
> > Honestly, I don't know how to fix it gracefully for non-DT case.
> > I can update commit message to mention that this is fix for DT case only.
> 
> no, that won't do :-) There are other users for this driver and they are
> all "out-of-compliance" when it comes to DMA usage. Apparently, the
> desired behavior is to pass correct device to DMA API which the gadget
> side is already doing (see below). For the host side, the fix has to be
> more involved.
> 
> Frankly, I'd prefer that DMA setup could be inherited from parent
> device, then it wouldn't really matter and a bunch of this could be
> simplified. Some sort of dma_inherit(struct device *dev, struct device
> *parent) would go a long way, IMHO.

I would be in favour of a dma_inherit() function as well. We could hack
something up in the arch code (like below) but I would rather prefer an
explicit dma_inherit() call by drivers creating such devices.

diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
index ba437f090a74..ea6fb9b0e8fa 100644
--- a/arch/arm64/include/asm/dma-mapping.h
+++ b/arch/arm64/include/asm/dma-mapping.h
@@ -29,8 +29,11 @@ extern struct dma_map_ops dummy_dma_ops;
 
 static inline struct dma_map_ops *__generic_dma_ops(struct device *dev)
 {
-	if (dev && dev->archdata.dma_ops)
-		return dev->archdata.dma_ops;
+	while (dev) {
+		if (dev->archdata.dma_ops)
+			return dev->archdata.dma_ops;
+		dev = dev->parent;
+	}
 
 	/*
 	 * We expect no ISA devices, and all other DMA masters are expected to

-- 
Catalin