[U-Boot] [RFC PATCH] usb: dwc2: handle bcm2835 phys->virt address translations

[Marek Vasut]

On Friday, March 13, 2015 at 05:35:53 PM, Stephen Warren wrote:
> On 03/13/2015 08:30 AM, Marek Vasut wrote:
> > On Friday, March 13, 2015 at 07:13:09 AM, Stephen Warren wrote:
> >> BCM2835 bus addresses use the top 2 bits to determine whether
> >> peripherals use or bypass the GPU L1 and L2 cache.
> >> BCM2835-ARM-Peripherals.pdf states that:
> >> 
> >> 0: L1 & L2 cached
> >> 4: L2 cache coherent (non allocaing)
> >> 8: L2 cached only
> >> c: Direct uncached.
> > 
> > Caches aren't working on BCM2xxx or what's the reason for this hack ?
> > Or are these different (not on-CPU) caches we're talking about (yes,
> > I did notice the GPU Lx cache stuff)?
> 
> Yes, the "GPU" has its own caches, entirely separate from the ARM core
> and at a different location in the system bus structure, and it seems as
> if at least some other peripherals other than GPU/graphics/VideoCore
> access DRAM via those caches too.
> 
> There are some brief details in BCM2835-ARM-Peripherals.pdf, although it
> isn't terribly clear.

Thanks for clearing this up. I suspect there's no way to turn those caches
off altogether, right ? But uh ... ew :(

Best regards,
Marek Vasut