linux-kernel - Re: [PATCH 1/2] drm/tegra: Set DMA ops

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Message-ID: <20160223152815.GD27656@ulmo>
Date:	Tue, 23 Feb 2016 16:28:15 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	Terje Bergström <tbergstrom@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org, gnurou@...il.com
Subject: Re: [PATCH 1/2] drm/tegra: Set DMA ops

On Tue, Feb 23, 2016 at 03:25:53PM +0900, Alexandre Courbot wrote:
> The current settings leaves the DRM device's dma_ops field NULL, which
> makes it use the dummy DMA ops on arm64 and return an error whenever we
> try to import a buffer. Call of_dma_configure() with a NULL node (since
> the device is not spawn from the device tree) so that
> arch_setup_dma_ops() is called and sets the default ioswtlb DMA ops.
> 
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> ---
>  drivers/gpu/drm/tegra/drm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
> index d347188bf8f4..bc0555adecaf 100644
> --- a/drivers/gpu/drm/tegra/drm.c
> +++ b/drivers/gpu/drm/tegra/drm.c
> @@ -9,6 +9,7 @@
>  
>  #include <linux/host1x.h>
>  #include <linux/iommu.h>
> +#include <linux/of_device.h>
>  
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_atomic_helper.h>
> @@ -990,6 +991,7 @@ static int host1x_drm_probe(struct host1x_device *dev)
>  		return -ENOMEM;
>  
>  	dev_set_drvdata(&dev->dev, drm);
> +	of_dma_configure(drm->dev, NULL);

Looking at the various pieces, I think this really belongs in
host1x_device_add() (see drivers/gpu/host1x/bus.c) where it can replace
the open-coded setting of DMA and coherent DMA masks. Also why can't we
pass the correct device tree node here? The DRM device is a virtual
device that hangs off the host1x device, so I think it could use the
same device tree node as the host1x device.

Something like the below (untested).

Thierry

--- >8 ---
diff --git a/drivers/gpu/host1x/bus.c b/drivers/gpu/host1x/bus.c
index c2e7fba370bb..d46d26a574da 100644
--- a/drivers/gpu/host1x/bus.c
+++ b/drivers/gpu/host1x/bus.c
@@ -17,6 +17,7 @@
 
 #include <linux/host1x.h>
 #include <linux/of.h>
+#include <linux/of_device.h>
 #include <linux/slab.h>
 
 #include "bus.h"
@@ -393,9 +394,8 @@ static int host1x_device_add(struct host1x *host1x,
 	INIT_LIST_HEAD(&device->list);
 	device->driver = driver;
 
-	device->dev.coherent_dma_mask = host1x->dev->coherent_dma_mask;
-	device->dev.dma_mask = &device->dev.coherent_dma_mask;
 	dev_set_name(&device->dev, "%s", driver->driver.name);
+	of_dma_configure(&device->dev, host1x->dev->of_node);
 	device->dev.release = host1x_device_release;
 	device->dev.bus = &host1x_bus_type;
 	device->dev.parent = host1x->dev;

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