On Thu, Oct 10, 2013 at 07:21:40AM +0200, Michal Simek wrote: > On 10/09/2013 05:25 PM, Sören Brinkmann wrote: > > On Tue, Oct 08, 2013 at 04:38:17PM +0100, Mark Rutland wrote: > >> On Tue, Oct 08, 2013 at 03:36:11PM +0100, Soren Brinkmann wrote: > >>> In some use cases Zynq's FPGA clocks are used as static clock > >>> generators for IP in the FPGA part of the SOC for which no Linux driver > >>> exists and would control those clocks. To avoid automatic > >>> gating of these clocks in such cases a new property - fclk-enable - is > >>> added to the clock controller's DT description to accomodate such use > >>> cases. It's value is a bitmask, where a set bit results in enabling > >>> the corresponding FCLK through the clkc. > >>> > >>> FPGA clocks are handled following the rules below: > >>> > >>> If an FCLK is not enabled by bootloaders, that FCLK will be disabled in > >>> Linux. Drivers can enable and control it through the CCF as usual. > >>> > >>> If an FCLK is enabled by bootloaders AND the corresponding bit in the > >>> 'fclk-enable' DT property is set, that FCLK will be enabled by the clkc, > >>> resulting in an off by one reference count for that clock. Ensuring it > >>> will always be running. > >>> > >>> The default value for 'fclk-enable' is '0xf' (all FCLK's enabled by the > >>> bootloader are enabled through the clkc. > >> > >> Why? Juding by the diff that's not what the code currently does, so why > >> not leave it as 0, and only set it where required as a work-around? > > The default is set as described here: > > [...] > >>> + ret = of_property_read_u32(np, "fclk-enable", &fclk_enable); > >>> + if (ret) > >>> + fclk_enable = 0xf; > >>> + > > > > The default has been chosen this way, because it avoids trouble with > > customers. Customers expect the FPGA clocks to be running, once they > > configured them in the FPGA tools. If Linux gates them off for some > > reason, it creates confusion and often ends up in customer support. > > But in general I agree. It is kind of a work around and having zero as > > default would be desirable. I'd leave this to Michal. > > No problem to have default value setup to 0. And use this workaround > when it is set in DTS. All right, I'll prepare v2 with that default changed to 0. Sören -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
