On 13 December 2010 16:29, Russell King - ARM Linux
<linux@xxxxxxxxxxxxxxxx> wrote:
> On Mon, Dec 13, 2010 at 03:52:20PM +0000, Catalin Marinas wrote:
>> On 10 December 2010 17:03, Russell King - ARM Linux
>> <linux@xxxxxxxxxxxxxxxx> wrote:
>> > On Fri, Dec 10, 2010 at 12:03:07PM +0100, Janusz Krzysztofik wrote:
>> >> Âvoid __init omap1_camera_init(void *info)
>> >> Â{
>> >> Â Â Â struct platform_device *dev = &omap1_camera_device;
>> >> + Â Â dma_addr_t paddr = omap1_camera_phys_mempool_base;
>> >> + Â Â dma_addr_t size = omap1_camera_phys_mempool_size;
>> >> Â Â Â int ret;
>> >>
>> >> Â Â Â dev->dev.platform_data = info;
>> >>
>> >> + Â Â if (paddr) {
>> >> + Â Â Â Â Â Â if (dma_declare_coherent_memory(&dev->dev, paddr, paddr, size,
>> >> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â DMA_MEMORY_MAP | DMA_MEMORY_EXCLUSIVE))
>> >
>> > Although this works, you're ending up with SDRAM being mapped via
>> > ioremap, which uses MT_DEVICE - so what is SDRAM ends up being
>> > mapped as if it were a device.
>>
>> BTW, does the generic dma_declare_coherent_memory() does the correct
>> thing in using ioremap()?
>
> I argue it doesn't, as I said above. ÂIt means we map SDRAM as device
> memory, and as I understand the way interconnects work, it's entirely
> possible that this may not result in the SDRAM being accessible.
[...]
> So, not only does this fail the kernel's own rules, but as we already know,
> it fails the architecture's restrictions with multiple mappings of memory
> when used with SDRAM, and it also maps main memory as a device. ÂI wonder
> how many more things this broken API needs to do wrong before it's current
> implementation is consigned to the circular filing cabinet.
Should we not try to fix the generic code and still allow platforms to
use dma_declare_coherent_memory() in a safer way? I guess it may need
some arguing/explanation on linux-arch.
--
Catalin
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