Hi Stephen, On Wed, 6 May 2015 23:39:53 -0700 Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote: > On 04/30, Boris Brezillon wrote: > > Clock rates are stored in an unsigned long field, but ->round_rate() > > (which returns a rounded rate from a requested one) returns a long > > value (errors are reported using negative error codes), which can lead > > to long overflow if the clock rate exceed 2Ghz. > > > > Change ->round_rate() prototype to return 0 or an error code, and pass the > > requested rate as a pointer so that it can be adjusted depending on > > hardware capabilities. > > > > Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> > > Tested-by: Heiko Stuebner <heiko@xxxxxxxxx> > > Tested-by: Mikko Perttunen <mikko.perttunen@xxxxxxxx> > > Reviewed-by: Heiko Stuebner <heiko@xxxxxxxxx> > > This patch is fairly invasive, and it probably doesn't even > matter for most of these clock providers to be able to round a > rate above 2GHz. Fair enough. > I've been trying to remove the .round_rate op > from the framework by encouraging new features via the > .determine_rate op. Oh, I wasn't aware of that (BTW, that's a good thing). Maybe this should be clearly stated (both in the struct clk_ops kerneldoc header and in Documentation/clk.txt). > Sadly, we still have to do a flag day and > change all the .determine_rate ops when we want to add things. Yes, but the number of clk drivers implementing ->determine_rate() is still quite limited compared to those implementing ->round_rate(). > > What if we changed determine_rate ops to take a struct > clk_determine_info (or some better named structure) instead of > the current list of arguments that it currently takes? Then when > we want to make these sorts of framework wide changes we can just > throw a new member into that structure and be done. I really like this idea, especially since I was wondering if we could pass other 'clk rate requirements' like the rounding policy (down, closest, up), or the maximum clk inaccuracy. > > It doesn't solve the unsigned long to int return value problem > though. We can solve that by gradually introducing a new op and > handling another case in the rounding path. If we can come up > with some good name for that new op like .decide_rate or > something then it makes things nicer in the long run. I like the > name .determine_rate though :/ Why not changing the ->determine_rate() prototype. As said above, the number of clk drivers implementing this function is still quite limited, and I guess we can have an ack for all of them. > > The benefit of all this is that we don't have to worry about > finding the random clk providers that get added into other > subsystems and fixing them up. If drivers actually care about > this problem then they'll be fixed to use the proper op. FYI, > last time we updated the function signature of .determine_rate we > broke a couple drivers along the way. > Hm, IMHO, adding a new op is not a good thing. I agree that it eases the transition, but ITOH you'll have to live with old/deprecated ops in your clk_ops structure with people introducing new drivers still using the old ops (see the number of clk drivers implementing ->round_rate() instead of ->determine_rate()). Best Regards, Boris -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
