[PATCH 1/1] arm/dts: Tegra30: Add device tree support for SMMU

From: Thierry Reding <redacted>
Subject: Re: [PATCH 1/1] arm/dts: Tegra30: Add device tree support for SMMU
Date: Wed, 18 Apr 2012 07:41:40 +0200
Message-ID: [off-list ref]

* PGP Signed by an unknown key

* Hiroshi Doyu wrote:

quoted

On Mon, 16 Apr 2012 17:34:19 +0200
Arnd Bergmann [off-list ref] wrote:

quoted

On Monday 16 April 2012, Hiroshi Doyu wrote:

quoted

What about using "dma-window" property to specify IOVA range in dtsi as below?

arch/powerpc/platforms/cell/iommu.c:

698 static int __init cell_iommu_get_window(struct device_node *np,
699                                          unsigned long *base,
700                                          unsigned long *size)
701 {
702         const void *dma_window;
703         unsigned long index;
704
705         /* Use ibm,dma-window if available, else, hard code ! */
706         dma_window = of_get_property(np, "ibm,dma-window", NULL);
707         if (dma_window == NULL) {          ^^^^^^^^^^^^^^
708                 *base = 0;
709                 *size = 0x80000000u;
710                 return -ENODEV;
711         }
712
713         of_parse_dma_window(np, dma_window, &index, base, size);
714         return 0;
715 }

Yes, that's the right way to do it, but I would use the more generic
"dma-window" name rather than "ibm,dma-window", which was originally
introduced for pseries and for some reason copied into the cell qs2x
firmware.

Which name is better, "dma-window" or "iova-window"?
Considering DMA IOMMU mapping API, "dma-window" may sound appropriate to me.

But the window isn't necessarily used for DMA transfers. I was going to
propose "aperture", but that doesn't seem quite right since it is a very
GART-specific term. "iova-window" sounds like the best fit for what it
really is.

If we can consider IOMMU as one of the implementation of DMA(Direct
Memory Access), the prefix "dma-(window)" may make sense here. Then,
we don't have to introduce a new concept "IO virtual address(iova)" in
addition to the existing "bus address"(?)

Anyway, either name would be ok for me;)