How to handle named resources with DT?

[Grant Likely]

On Tue, Aug 09, 2011 at 07:47:20PM +0200, Cousson, Benoit wrote:
> On 8/9/2011 7:23 PM, Grant Likely wrote:
> >On Tue, Aug 9, 2011 at 10:57 AM, Cousson, Benoit<b-cousson at ti.com>  wrote:
> >>Hi Manju,
> >>
> >>On 8/9/2011 6:29 PM, G, Manjunath Kondaiah wrote:
> >>>
> >>>Hi Benoit,
> >>>
> >>>On Tue, Aug 09, 2011 at 11:23:20AM +0200, Cousson, Benoit wrote:
> >>>>
> >>>>Hi Grant,
> >>>>
> >>>>Trying to bind hwmod informations with DT, I'm facing a little
> >>>>limitation.
> >>>>A bunch of drivers are using the platform_get_resource_byname, so
> >>>>the name for the resource is needed.
> >>>>
> >>>>The name is used so far for IORESOURCE_MEM, IORESOURCE_IRQ and
> >>>>IORESOURCE_DMA types of resources.
> >>>
> >>>IORESOURCE_MEM and IORESOURCE_IRQ's are fetched from dt blob and
> >>>it will be part of pdev.
> >>
> >>Yes, but without the proper name in the resource structure. It will be then
> >>impossible to use the platform_get_resource_byname function that is
> >>currently used by a bunch of drivers.
> >
> >There is no analogous mechanism for _byname in the device tree.  The
> >DT binding for a device must explicitly state what order the register
> >ranges are in.  The driver will need to be adapted.
> 
> That seems to be a small regression for my point of view. Relying on
> the order is not super safe. This is not very readable either.
> That's for that exact reason that we changed our drivers to use
> platform_get_resource_byname. That's probably the reason why that
> API is there as well.
> For the same IP, the number of entries can vary depending of the SoC
> revision.
> By using the _byname, we can check if the resource is there or not
> without having to care about the position.

We've done it that way for a very long time with the device tree.  If
you want to do something by name, then propose a binding that will
make it work alongside the existing scheme.

> 
> >>>For IORESOURCE_DMA, you can have property
> >>>"dma-channel" in dtsi file and fetch dma-channel in driver probe
> >>>through "of_property_read_u32()" api.
> >>
> >>That will not be enough to get the name. So maybe something like:
> >>        dmas =<12>, "rx_req",<13>, "tx_req";
> >>will be doable.
> >>The issue is that the name is optional so managing the multiple entries
> >>might be tricky.
> >
> >DMA channels will never show up in the resource structure anyway.
> 
> Can you elaborate on that point? AFAIK, IORESOURCE_DMA is already
> used today.

IORESOURCE_DMA is a Linux construct, as is IORESOURCE_IRQ and
IORESOURCE_MEM.  However, IRQ and MEM can be directly mapped from the
common 'reg' and 'interrupts' bindings used by pretty much all device
tree nodes.  Therefore common code can be written to translate MEM and
IRQ that will always work.  There is no such common binding in place
for DMA regions, so common setup code cannot do it transparently for
the device driver.

g.