On Thu, Mar 28, 2013 at 7:18 AM, Tony Prisk <li...@prisktech.co.nz> wrote: > On Wed, 2013-03-27 at 23:09 -0600, Stephen Warren wrote: >> Use the new standard API of_property_read_u32_index() instead of open- >> coding it. >> >> Signed-off-by: Stephen Warren <swar...@wwwdotorg.org> >> --- >> Note: This depends on the proposed patch "of: Add support for reading >> a u32 from a multi-value property" by Tony Prisk. >> >> BTW, I realized why I didn't create that standard API, but wrote custom >> prop_u32() instead; the code has already looked up the properties, and >> validated their length, so prop_u32() can simply index into the property >> data, whereas of_property_read_u32_index() needs to go search for the >> property and re-validate it every time, so there's a bunch more overhead. >> It also means duplicating the property name, although I could use a >> define for that. I'm not entirely convinced that using this standard API >> is a win in this case. LinusW, Tony, what do you think? >> --- > > When I was writing the function I had a similar thought about the fact > we need to work out the length first, which as you mentioned, requires > all the prior work on the property anyway. > > I didn't bring it up, because I thought someone might say 'hey, you > should add a function to get the count as well' :) > > In both the brcm and vt8500 use cases, we will have the issue of > multiple lookups on the same property using 'generic' functions. Price > we have to pay for generic code?
My take on this is that if you look in for example: drivers/of/platform.c you find that for every node in the device tree when it creates a platform device with a resource it will for example call of_address_to_resource() twice. The same for IRQs IIRC. So basically this behaviour is inherent in all OF/DT code, and no point trying to work around it. I don't know if there is a way to fix the problem at the root, like have the DT parser annotate nodes with the number of resources of each type (like a decorated tree) so it can be looked up quickly somehow. I'm not smart enough on DT for such things... Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
