Re: FOR COMMENT: void __iomem * and similar casts are Bad News

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Sep 03, 2008 at 04:04:11PM -0400, Eduardo Valentin wrote:
> Hi Russell,
> 
> On Wed, Sep 3, 2008 at 3:48 PM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > Yes, that will be virtual.  But what does it mean to call:
> >
> >        omap_set_dma_dest_params()
> >
> > specifying a virtual address?  Can the DMA controller cope with DMAing
> > to virtual addresses?  My hunch is that the DMA controller can't cope
> > with that, so giving it a virtual address is a bug.
> >
> > Let me change the question: does omap_set_dma_dest_params()'s 4th
> > argument take a virtual or a physical address?  If the former, it's
> > prototype is wrong, and its 4th argument needs to be typed as
> > 'void __iomem *' rather than 'unsigned long'.  If the latter, the code
> > above is wrong.
> >
> > Do you see what I'm getting at now?
> 
> Ok. I got your point. I took a look at it and it expects a virtual address
> on its 4th argument.

I'm sorry, but I don't think you have.

> I uses it with dma_write() macro, which uses it with __raw_write()
> (arch/arm/plat-omap/dma.c).

That's true, but probably not in the way which would require it to be
a virtual address that you're thinking.

void omap_set_dma_dest_params(int lch, int dest_port, int dest_amode,
                              unsigned long dest_start,
                              int dst_ei, int dst_fi)
{
        if (cpu_class_is_omap1()) {
                dma_write(dest_start >> 16, CDSA_U(lch));
                dma_write(dest_start, CDSA_L(lch));
        }

        if (cpu_class_is_omap2())
                dma_write(dest_start, CDSA(lch));
}

'dest_start' is a value to be written to the hardware registers in
the DMA controller.  So, the question now is: do the CDSA registers
expect a virtual or a physical address to be written to them?

I would look up this CDSA register in the OMAP manuals, if they were
accessible... Are they not publically available?  (Google isn't
helping, neither is searching on ti.com...)