linux-kernel - Re: [PATCH v8 1/4] pci:host: APM X-Gene PCIe host controller driver

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Message-ID: <20140917160337.GA15261@e104818-lin.cambridge.arm.com>
Date:	Wed, 17 Sep 2014 17:03:39 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Tanmay Inamdar <tinamdar@....com>
Cc:	Liviu Dudau <Liviu.Dudau@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Rob Landley <rob@...dley.net>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@....com" <patches@....com>,
	"jcm@...hat.com" <jcm@...hat.com>
Subject: Re: [PATCH v8 1/4] pci:host: APM X-Gene PCIe host controller driver

On Tue, Sep 16, 2014 at 09:02:11PM +0100, Tanmay Inamdar wrote:
> On Fri, Sep 12, 2014 at 2:18 AM, Liviu Dudau <Liviu.Dudau@....com> wrote:
> > On Thu, Sep 11, 2014 at 11:57:43PM +0100, Tanmay Inamdar wrote:
> >> This patch adds the AppliedMicro X-Gene SOC PCIe host controller driver.
> >> X-Gene PCIe controller supports maximum up to 8 lanes and GEN3 speed.
> >> X-Gene SOC supports maximum 5 PCIe ports.
> >>
> >> Signed-off-by: Tanmay Inamdar <tinamdar@....com>
> >
> > It looks good to me now. You can add if you care:
> >
> > Reviewed-by: Liviu Dudau <Liviu.Dudau@....com>
> 
> I will have to send another version of patch as I forgot to add
> 'dma-coherent' in device tree entry.
> 
> Secondly I see that setting 'dma-coherent' in device tree node sets
> coherent_dma_ops for the root bus but for the endpoint another 'dev'
> gets assigned. This causes endpoint to use non-coherent dma apis
> causing failure in dma operations.

For PCIe, setting dma-coherent in the DT nodes wouldn't have any effect
yet. We have of_dma_configure() being called for platform devices but it
won't work for PCIe which are probed at run-time (nor for AMBA which
require an additional patch).

So for arm64 currently we have some hooks in dma-mapping.c to intercept
when a device is added to a bus. What I need to do though is check
recursively whether the parent (bus) had the 'dma-coherent' property
(pointed out by Jon). I think something like this would do (not tested):

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 4164c5ace9f8..638475378f94 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -316,7 +316,7 @@ static int dma_bus_notifier(struct notifier_block *nb,
 	if (event != BUS_NOTIFY_ADD_DEVICE)
 		return NOTIFY_DONE;
 
-	if (of_property_read_bool(dev->of_node, "dma-coherent"))
+	if (of_dma_is_coherent(dev->of_node))
 		set_dma_ops(dev, &coherent_swiotlb_dma_ops);
 
 	return NOTIFY_OK;

After this, we need to a bus notifier for PCIe as well. Since I don't
think we have an of_node for a PCI device, we would need to check
recursively on the parent device rather than the parent node until we
find an OF node with the 'dma-coherent' property.

-- 
Catalin
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