Hi > that takes the MMC clock (and only the MMC clock) and does the setup > (it's basically configuring two values, "sample" and "output", into the > clock register). I really don't know what does this do/why is it > required/when is it used; I'm cc'ing Hans and David who can hopefully > explain that part. Since the read/write operations have to happen asynchronously and in a manner so that the data provided by the SD-Card can be fetched on time, a specific clock phase shift is required as you can see in the linked picture[1]. That's what the function is doing: It accesses the special registers of the MMC clock device and configures this phase offset. > I also saw a similar requirement from the gmac people (on cc too), who > needed to set the phy type (or something like that) on one of the clock > registers; so I'm thinking maybe a generic "tune something" approach > that lets users configure some clock-dependent, arbitrary aspect of the > clock is the way forward. Otherwise, we're going to end up bloating the > clock framework with a lot of callback pointers that are going to be > used in one or two clocks out of potentially hundreds on the whole system. It totally makes sense, since GMAC will be doing asynchrous operations as well. -David [1] http://www.chipestimate.com/techtalk/images/11022010_fig2_3.JPG
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