On Mon, Aug 08, 2011 at 04:19:20PM +0200, Marc Kleine-Budde wrote: > On 08/08/2011 04:03 PM, Robin Holt wrote: > > On Mon, Aug 08, 2011 at 03:44:36PM +0200, Marc Kleine-Budde wrote: > >> On 08/08/2011 03:08 PM, Wolfgang Grandegger wrote: > >>> On 08/08/2011 01:31 PM, Robin Holt wrote: > >>>> On Mon, Aug 08, 2011 at 10:37:58AM +0200, Wolfgang Grandegger wrote: > >>>>> On 08/06/2011 04:34 PM, Robin Holt wrote: > >>>>>> flexcan driver needs the clk_get, clk_get_rate, etc functions > >>>>>> to work. This patch provides the minimum functionality. > >>>>> > >>>>> This needs some more general thoughts... apart from the question where > >>>>> the code should go. > >>>>> > >>>>> Like for the MSCAN on the MPC5200, the user should be *able* to select > >>>>> an appropriate clock source and divider via DTS node properties. > >>>>> Currently it seems, that the DTS properties must match some > >>>>> pre-configured values, most likely set by the boot loader. Please > >>>>> correct me if I'm wrong. For me this is generic and should go into the > >>>>> Flexcan driver. From there, a platform specific function, e.g. > >>>>> flexcan_set_clock() might be called. > >>>> > >>>> OK. Dug a bit more. The p1010 built-in clocksource seems to be the > >>>> periphereal clock frequency which is system bus frequency divided > >>>> by 2. The clock source can not be changed, but the clock divider can > >>>> by freezing the interface and setting the CTRL register. This appears > >>>> to only be done by the boot loader. I do not see why we can not leave > >>> > >>> And likely Freescale's bootloader does also fixup the DTS Flexcan node. > >>> Ah, oh, there's already someting in the mainline U-BOOT: > >>> > >>> commit 65bb8b060a873fa4f5188f2951081f6011259614 > >>> Author: Bhaskar Upadhaya <bhaskar.upadh...@freescale.com> > >>> Date: Fri Mar 4 20:27:58 2011 +0530 > >>> > >>> powerpc/85xx: Fix up clock_freq property in CAN node of dts > >>> > >>> Fix up the device tree property associated with the Flexcan clock > >>> frequency. This property is used to calculate the bit timing > >>> parameters > >>> for Flexcan. > >>> > >>> Signed-off-by: Bhaskar Upadhaya <bhaskar.upadh...@freescale.com> > >>> Signed-off-by: Kumar Gala <ga...@kernel.crashing.org> > >>> > >>> > >>>> that functionality in the boot loader and then go back to a variation > >>>> on my earlier flexcan_clk_* patch. Is that close to the direction you > >>>> think we should go or have I completely misunderstood your wishes? > >>> > >>> The boot loader might not chose the optimum clock source and frequency, > >>> which might even be application dependent. Therefore it would be nice to > >>> allow the user to change it if necessary. Some CAN interfaces do even > >>> allow to use an external clock source. The main question is where we add > >>> that functionality. As more as I think of it, the clock interface would > >>> not be that bad, especially if it's available. > >>> > >>> Furthermore, if the bootloader sets the clock source and divider, we do > >>> not need device tree properties for it. A simply register lookup would > >>> reveal what values are used. We may just need the input clock source. > >> > >> If the bootloader touches the divider _in_ the flexcan core, that would > >> make absolutely no sense. The clock divider in the flexcan core (in the > >> CTRL register) is the bitrate pre-scaler calculated by the bit-timing > >> algorithm. > >> > >> What we need in the device tree is, from my point of view. > >> a) the used clock source (bus clock or xtal clock) > >> b) the frequency of that clock > >> > >> These problems are solved on arm via: > >> a) bus clock is hard coded [1] > >> b) get that clock frequency via clk_get_rate(). > > > > Just to make sure I understand correctly, the clk_get_rate() return > > value comes from the device tree and a mach specific handler, right? > > And 'mach-specific' really means what, a processor family? > > I'm talking about the mainline driver, that has no device tree support. > The clock stuff on arm currently goes like this:
What is the difference between device tree support and the clkdev based clock sources using of_match to find a clock source for a particular device. It looks to me like those are filled in based upon device tree information, but I _TRULY_ do not know what I am talking about. > The driver asks for the clock related to the device. The architecture > code has previously connected the flexcan device to an arch specific > (i.mx25, i.mx35) clock. That clock is returned. Enable/disable/get_rate > are working on that specific clock. I will go and study that some more. I did my cross-compile using mxs_defconfig. Is there a better config I should be using? I typically compile a kernel with the drivers I desire and then build my cscope database using the files used in that build. Thanks, Robin _______________________________________________ Socketcan-core mailing list Socketcan-core@lists.berlios.de https://lists.berlios.de/mailman/listinfo/socketcan-core
