Re: [PATCH v2 1/2] clk: qcom: Add display clock controller driver for QCM2290

[Stephen Boyd <sboyd@kernel.org>]

Quoting Loic Poulain (2021-12-16 11:21:51)
> Hi Stephen,
> 
> 
> On Thu, 16 Dec 2021 at 04:49, Stephen Boyd <sboyd@kernel.org> wrote:
> >
> > Quoting Loic Poulain (2021-12-09 06:09:10)
> > > diff --git a/drivers/clk/qcom/dispcc-qcm2290.c b/drivers/clk/qcom/dispcc-qcm2290.c
> > > new file mode 100644
> > > index 00000000..8aa5d31
> > > --- /dev/null
> > > +++ b/drivers/clk/qcom/dispcc-qcm2290.c
> > > @@ -0,0 +1,602 @@
> > > +// SPDX-License-Identifier: GPL-2.0-only
> > > +/*
> > > + * Copyright (c) 2020, The Linux Foundation. All rights reserved.
> > > + * Copyright (c) 2021, Linaro Ltd.
> > > + */
> > > +
> [...]
> > > +static struct clk_rcg2 disp_cc_mdss_pclk0_clk_src = {
> > > +       .cmd_rcgr = 0x205c,
> > > +       .mnd_width = 8,
> > > +       .hid_width = 5,
> > > +       .parent_map = disp_cc_parent_map_4,
> > > +       .clkr.hw.init = &(struct clk_init_data){
> > > +               .name = "disp_cc_mdss_pclk0_clk_src",
> > > +               .parent_data = disp_cc_parent_data_4,
> > > +               .num_parents = ARRAY_SIZE(disp_cc_parent_data_4),
> > > +               .flags = CLK_SET_RATE_PARENT | CLK_GET_RATE_NOCACHE | CLK_OPS_PARENT_ENABLE,
> >
> > These last two flags are needed for what?
> 
> NOCACHE is probably useless with mainline.

Ok then please remove it.

> 
> I've added OPS_PARENT_ENABLE because AFAIU changing clock rate can
> lead to parent switch, and parent switch can only be done if parent
> clocks are enabled for rcg2 clocks. Otherwise the update fails and we
> get the following:
>     disp_cc_mdss_pclk0_clk_src: rcg didn't update its configuration.
>     WARNING: CPU: 2 PID: 77 at drivers/clk/qcom/clk-rcg2.c:122
> update_config+0xe0/0xf0
> 
> I'm a bit surprised other similar dispcc drivers don't use the same
> flags though.

That's quite odd. We migrate the prepare and enable count to the new
parent in the core framework so is the rcg on, but doesn't look like it
is on to the core and set_rate is being called?