[RFC] usb issue on imx27: 3 clocks are needed

[peter.chen@freescale.com (Peter Chen)]

On Mon, Aug 18, 2014 at 01:49:03PM +0200, gwenhael.goavec wrote:
> On Mon, 18 Aug 2014 10:35:53 +0000
> Peter Chen <Peter.Chen@freescale.com> wrote:
> 
> >  
> > > On Mon, Aug 18, 2014 at 05:00:59PM +0800, Peter Chen wrote:
> > > > On Sat, Aug 16, 2014 at 05:38:30PM +0200, Philippe Reynes wrote:
> > > > > Hi all,
> > > > >
> > > > > i.MX27's usb needs three clocks (usb_ipg_gate, usb_ahb_gate and
> > > > > usb_div) but the current chipidea driver implementation, and
> > > > > devicetree, provides only ipg and ahb. Consequently, if the
> > > > > bootloader don't enable the last one, the kernel will crash.
> > > > >
> > > > > Our approach/idea is to add a second, optionnal, clock in
> > > > > ci_hdrc_imx.c with 'per' name in devicetree  and to add  clock name
> > > 'main_clk' for mandatory clock.
> > > > > This approach it correct? Or an other approach seems better?
> > > > > Thank you very much for your point of view.
> > > > >
> > > >
> > > > It is ok for me to have ipg, ahb and per clocks at driver, but how can
> > > > you maintain DT consistent?
> > > 
> > > Adding new clock as optional one will just maintain the DT compatibility.
> > > 
> > 
> > How to handle node_usb_soc1's clock which is without clk name to consistent with three
> > clocks for node_usb_soc2 at driver? Except for adding some platform judge code at
> > driver, do you have other solutions?
> > 
> > node_usb_soc1: {
> > 	clocks = <&clks IMX6_CLK_USBOH3>;
> > };
> > 
> > node_usb_soc2: {
> > 	clocks = <&clks IMX27_CLK_USBIPG>, <&clks IMX27_CLK_USBOH3>, <&clks IMX27_CLK_USBPER>;
> > 	clock-names = "ipg", "ahb", "per";
> > };
> > 
> > Peter
> > --
> 
> Our idea is something like this :
> node_usb_soc: {
> 	clocks = <&clks IMX27_CLK_USBxxx>;
> 	clock-names = "main_clk";
> };
> for all CPUs
> 
> and 
> node_usb_imx27: {
> 	clocks = <&clks IMX27_CLK_USB_IPG_GATE>,
> 		<&clks IMX27_CLK_USB_DIV>;
> 	clock-names = "main_clk", "per";
> };
> 
> For imx27 and CPUs with the need of more than one clock.
> 

Just like Shawn said, it breaks DT compatibility, how the old dtb works
with newer version kernel after you change.

> The last clock (ie ahb) is handled by usbmisc.c and if "per" clock is not
> present in the dtsi chipidea will not fails, just setting data->per_clk = NULL
> for prepare/unprepare.
> 
> Gwenhael

-- 
Best Regards,
Peter Chen