Hello, On 2014-02-26 13:14, Grant Likely wrote:
On Fri, 21 Feb 2014 13:25:22 +0100, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote: > Use recently introduced of_reserved_mem_device_init() function to > automatically assign respective reserved memory region to the newly created > platform and amba device. > > Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> I'm wary on this patch. It hides the assignment of regions into the core code and I worry that it is the wrong level of abstraction. I would think that drivers should know that they need a reserved memory region and should be calling the API to obtain the region directly rather than doing it for them. The reason being is that there may be some situations where the common code isn't quite right and the driver needs to override the behaviour. If it is called automatically then the driver cannot do that. Is it really a big burden to have the driver call the reserved memory init function?
If a device requires very special handling of the reserved memory region, it may simply provide its own reserved memory region driver which will do the required early initialization. If we assume that driver needs to initialize reserved region manually, then why do we ever bother with adding support for custom reserved memory drivers and assigning regions to a device node? We can simply stick with just a set of reserved regions and tell drivers to use them. In my opinion for most typical use cases a board designer will assign 'dma-shared-pool' driver to the given set of devices, which in turn ensures that all memory allocations for dma purposes for those device will be served from that region. It is really not a driver role to initialize it in such case. Driver should focus on controlling hw operations, regardless the way the hardware module has been integrated to the system. I can perfectly imagine a generic driver which operates the same way in any of the following cases (depends mainly on the hw version): 1) restricted dma window, 2) iommu for all dma for the given device, 3) fully featured memory master for dma for the given device (no restrictions), if the respective kernel subsystems did the correct initialization and provide their own methods for managing DMA operation. I already have a working platform glue code for the above cases tested with Samsung multimedia drivers. No changes to the drivers were required. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
