On Thu, Apr 30, 2015 at 11:31:22AM -0400, Rhyland Klein wrote: > On 4/30/2015 6:12 AM, Peter De Schrijver wrote: > > On Wed, Apr 29, 2015 at 01:21:46PM -0400, Rhyland Klein wrote: > >> From: Bill Huang <bilhuang@xxxxxxxxxx> > >> > >> Add logic which (if specified for a pll) can verify that a PLL is set > >> to the proper default value and if not can set it. This can be > >> specified per PLL as each will have different default values. > >> > > > > Why can't we just set the default values at init time? > > Sorry, I did some investigation into this and wrote up a nice response > ... and forgot to hit send ... > > The reason this can't be run only once at init time is the following. In > reality, we want to have the defined default values written as early as > possible. Idealy, the bootloader could write these, so the kernel need > only check, see they are right, and not touch them. However, since we > can't rely on the bootloader to do so, the kernel needs the support to > be able to write these default values. At init time, some pll's will be > enabled (from bootloader) and because they are enabled (and the rest of > the clk framework isn't done being setup yet) we can't disable them to > write the full register values. Therefore, the set_defaults logic uses a > 2-pass system. > > first pass: Try to set defaults at init/registration time. If pll is > disabled, this works fine. If it is enabled, then we update a subset of > the register as a "best effort" setting of the defaults. > > second pass: Should only run the first time we go through set_rate for a > pll. If the first pass already wrote default value, then it skips this > step. Otherwise it will go in, once the pll is disabled in the set_rate > path, and write the full register default. > > This is required because some registers need to be reset to the default > values we have to ensure locking works correctly. Does that make sense? Ok. I see... Should we print a warning (pr_warn()) the bootloader isn't initializing the hw correctly if the second pass needs to write the default values? Thanks, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
