linux-kernel - Re: [PATCH] clk: rockchip: rk3288: Limit use of USB PHY clock to USB

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Date:   Thu, 11 Apr 2019 17:16:57 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Heiko Stübner <heiko@...ech.de>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH] clk: rockchip: rk3288: Limit use of USB PHY clock to USB

Hi Heiko,

On Thu, Apr 11, 2019 at 09:03:07PM +0200, Heiko Stübner wrote:
> Hi Matthias,
> 
> Am Donnerstag, 11. April 2019, 19:59:17 CEST schrieb Matthias Kaehlcke:
> > The USB PHY clock can be configured as (grand) parent of uart0_sclk and
> > sclk_gpu. It has been observed that UART0 doesn't work reliably in high
> > speed mode with the PHY clock as input when certain USB devices are
> > plugged to the USB HOST1 port (see https://crrev.com/c/320543).
> > 
> > Prefix the name of the PHY clock with a '.' in the non-USB muxes to
> > effectively remove the clock as input from these muxes.
> > 
> > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > ---
> >  drivers/clk/rockchip/clk-rk3288.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/clk/rockchip/clk-rk3288.c b/drivers/clk/rockchip/clk-rk3288.c
> > index 5a67b7869960..677bc5485201 100644
> > --- a/drivers/clk/rockchip/clk-rk3288.c
> > +++ b/drivers/clk/rockchip/clk-rk3288.c
> > @@ -200,8 +200,8 @@ PNAME(mux_aclk_cpu_src_p)	= { "cpll_aclk_cpu", "gpll_aclk_cpu" };
> >  PNAME(mux_pll_src_cpll_gpll_p)		= { "cpll", "gpll" };
> >  PNAME(mux_pll_src_npll_cpll_gpll_p)	= { "npll", "cpll", "gpll" };
> >  PNAME(mux_pll_src_cpll_gpll_npll_p)	= { "cpll", "gpll", "npll" };
> > -PNAME(mux_pll_src_cpll_gpll_usb480m_p)	= { "cpll", "gpll", "usbphy480m_src" };
> > -PNAME(mux_pll_src_cpll_gll_usb_npll_p)	= { "cpll", "gpll", "usbphy480m_src", "npll" };
> > +PNAME(mux_pll_src_cpll_gpll_usb480m_p)	= { "cpll", "gpll", ".usbphy480m_src" };
> > +PNAME(mux_pll_src_cpll_gll_usb_npll_p)	= { "cpll", "gpll", ".usbphy480m_src", "npll" };
> 
> In general I like to have things like the clock-tree described fully
> and let the kernel handle correct sourcing ... but:
> 
> As you write this seems like a systemic problem when just connecting
> random peripherals can create unstable clock source frequencies,
> so I tend to agree here ... but:
> 
> Can we please find a more "talking" name for this ... because as with the
> above someone will find the "." and submit a fix for it ;-) .
> 
> So just name it "unstable_dummy" or so?

I looked for some common pattern, but couldn't find one. I liked the
'.' since it leaves the name of the clock mostly intact, just hiding
it (similar to a leading '.' in a Linux file system). But I agree that
it might not be expressive enough. I still like the idea to keep the
clock name around for reference, maybe we could name it
"unstable:usbphy480m_src" or similar. If you don't object I'll send a
patch with this some time tomorrow.

Thanks

Matthias