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Date: Thu, 30 Apr 2020 13:00:55 +0300
From: Abel Vesa <abel.vesa@....com>
To: Peng Fan <peng.fan@....com>
Cc: Aisheng Dong <aisheng.dong@....com>,
"shawnguo@...nel.org" <shawnguo@...nel.org>,
"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
Leonard Crestez <leonard.crestez@....com>,
"sboyd@...nel.org" <sboyd@...nel.org>,
"kernel@...gutronix.de" <kernel@...gutronix.de>,
"festevam@...il.com" <festevam@...il.com>,
dl-linux-imx <linux-imx@....com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Anson Huang <anson.huang@....com>,
Daniel Baluta <daniel.baluta@....com>,
"aford173@...il.com" <aford173@...il.com>,
Jacky Bai <ping.bai@....com>, Jun Li <jun.li@....com>,
"l.stach@...gutronix.de" <l.stach@...gutronix.de>,
"andrew.smirnov@...il.com" <andrew.smirnov@...il.com>,
"agx@...xcpu.org" <agx@...xcpu.org>,
"angus@...ea.ca" <angus@...ea.ca>,
"heiko@...ech.de" <heiko@...ech.de>,
Andy Duan <fugang.duan@....com>,
"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
Subject: Re: [PATCH V2 07/10] clk: imx: add mux ops for i.MX8M composite clk
On 20-04-27 09:11:56, Peng Fan wrote:
> > Subject: RE: [PATCH V2 07/10] clk: imx: add mux ops for i.MX8M composite
> > clk
> >
> > > From: Peng Fan <peng.fan@....com>
> > > Sent: Thursday, March 12, 2020 6:20 PM
> > >
> > > The CORE/BUS root slice has following design, simplied graph:
> > > The difference is core not have pre_div block.
> > > A composite core/bus clk has 8 inputs for mux to select, saying clk[0-7].
> > >
> > > SEL_A GA
> > > +--+ +-+
> > > | +->+ +------+
> > > CLK[0-7]--->+ | +-+ |
> > > | | | +----v---+ +----+
> > > | +--+ |pre_diva+----> | +---------+
> > > | +--------+ |mux +--+post_div |
> > > | +--+ |pre_divb+--->+ | +---------+
> > > | | | +----^---+ +----+
> > > +--->+ | +-+ |
> > > | +->+ +------+
> > > +--+ +-+
> > > SEL_B GB
> > >
> > > There will be system hang, when doing the following steps:
> > > 1. switch mux from clk0 to clk1
> > > 2. gate off clk0
> > > 3. swtich from clk1 to clk2, or gate off clk1
> > >
> > > Step 3 triggers system hang.
> >
> > Why Step 3 triggers system hang? Is this a HW limitation?
>
> It is what hardware designed.
>
> There is a counter inside the clk root module to choose
> SEL_A or SEL_B. If choose SEL_B, the parent of SEL_B must
> be active, otherwise the change from SEL_A to SEL_B
> will cause hang.
>
> SEL_A and SEL_B is inside the clock root module,
> It is not clk's software parentA/B. misunderstand
> this will misunderstand the whole fix.
>
> >
> > >
> > > If we skip step2, keep clk0 on, step 3 will not trigger system hang.
> > > However we have CLK_OPS_PARENT_ENABLE flag, which will unprepare
> > > disable the clk0 which will not be used.
> > >
> > > To address this issue, we could use following simplied software flow:
> > > After the first target register set
> > > wait the target register set finished
> > > set the target register set again
> > > wait the target register set finished
> > >
> > > The upper flow will make sure SEL_A and SEL_B both set the new mux,
> > > but with only one path gate on.
> > >
> > > And there will be no system hang anymore with step3.
> >
> > Is this IC proposed solution?
>
> This is what I proposed and IC team confirmed.
>
> >
> > >
> > > Signed-off-by: Peng Fan <peng.fan@....com>
> > > ---
> > >
> > > V2:
> > > Drop wait after write, add one line comment for write twice.
> > >
> > > drivers/clk/imx/clk-composite-8m.c | 62
> > > +++++++++++++++++++++++++++++++++++++-
> > > 1 file changed, 61 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/clk/imx/clk-composite-8m.c
> > > b/drivers/clk/imx/clk-composite-8m.c
> > > index 99773519b5a5..eae02c151ced 100644
> > > --- a/drivers/clk/imx/clk-composite-8m.c
> > > +++ b/drivers/clk/imx/clk-composite-8m.c
> > > @@ -24,6 +24,12 @@
> > >
> > > #define PCG_CGC_SHIFT 28
> > >
> > > +#define PRE_REG_OFF 0x30
> > > +#define PRE_MUXA_SHIFT 24
> > > +#define PRE_MUXA_MASK 0x7
> > > +#define PRE_MUXB_SHIFT 8
> > > +#define PRE_MUXB_MASK 0x7
> >
> > Are those macros used somewhere?
>
> Remove in v3.
>
> >
> > > +
> > > static unsigned long imx8m_clk_composite_divider_recalc_rate(struct
> > > clk_hw *hw,
> > > unsigned long parent_rate)
> > > {
> > > @@ -124,6 +130,57 @@ static const struct clk_ops
> > > imx8m_clk_composite_divider_ops = {
> > > .set_rate = imx8m_clk_composite_divider_set_rate,
> > > };
> > >
> > > +static u8 imx8m_clk_composite_mux_get_parent(struct clk_hw *hw) {
> > > + struct clk_mux *mux = to_clk_mux(hw);
> > > + u32 val;
> > > +
> > > + val = readl(mux->reg) >> mux->shift;
> > > + val &= mux->mask;
> > > +
> > > + return clk_mux_val_to_index(hw, mux->table, mux->flags, val); }
> >
> > You don't have to redefinition them if they're the same as clk_mux_ops.
> > You have the access to clk_mux_ops.
>
> This will require export_symbol of clk_mux_ops callbacks.
>
Maybe you can do here:
return clk_mux_ops.get_parent(hw);
> >
> > > +
> > > +static int imx8m_clk_composite_mux_set_parent(struct clk_hw *hw, u8
> > > +index) {
> > > + struct clk_mux *mux = to_clk_mux(hw);
> > > + u32 val = clk_mux_index_to_val(mux->table, mux->flags, index);
> > > + unsigned long flags = 0;
> > > + u32 reg;
> > > +
> > > + if (mux->lock)
> > > + spin_lock_irqsave(mux->lock, flags);
> > > +
> > > + reg = readl(mux->reg);
> > > + reg &= ~(mux->mask << mux->shift);
> > > + val = val << mux->shift;
> > > + reg |= val;
> > > + /* write twice to make sure SEL_A/B point the same mux */
> > > + writel(reg, mux->reg);
> > > + writel(reg, mux->reg);
> >
> > Why this affects both SEL_A/B?
>
> The internal counter will make sure both SEL_A/B point
> to the same mux.
>
> > Very tricky and may worth more comments.
>
> Ah, I think RM should be clear about the target interface
> and non-target interface.
>
> When you write once, saying use SEL_A, when
> you write the 2nd, the hardware will use SEL_B,
> when you write 3rd, the hardware will use SEL_A.
> and ...
>
This is a very interesting behavior from HW point of view.
So every write changes the mux ?
Unless there is an ERRATA for this, we'll get a lot of pushback from upstream.
> >
> > Besides that, I'd like to see Abel's comments on this patch.
>
>
> Abel,
>
> Any comments?
>
> Thanks,
> Peng.
>
> >
> > Regards
> > Aisheng
> >
> > > +
> > > + if (mux->lock)
> > > + spin_unlock_irqrestore(mux->lock, flags);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static int
> > > +imx8m_clk_composite_mux_determine_rate(struct clk_hw *hw,
> > > + struct clk_rate_request *req) {
> > > + struct clk_mux *mux = to_clk_mux(hw);
> > > +
> > > + return clk_mux_determine_rate_flags(hw, req, mux->flags); }
> >
> > Same as bove.
> >
> > > +
> > > +
> > > +const struct clk_ops imx8m_clk_composite_mux_ops = {
> > > + .get_parent = imx8m_clk_composite_mux_get_parent,
> > > + .set_parent = imx8m_clk_composite_mux_set_parent,
> > > + .determine_rate = imx8m_clk_composite_mux_determine_rate,
> > > +};
> > > +
> > > struct clk_hw *imx8m_clk_hw_composite_flags(const char *name,
> > > const char * const *parent_names,
> > > int num_parents, void __iomem *reg, @@ -136,6
> > > +193,7 @@ struct clk_hw *imx8m_clk_hw_composite_flags(const char
> > > +*name,
> > > struct clk_gate *gate = NULL;
> > > struct clk_mux *mux = NULL;
> > > const struct clk_ops *divider_ops;
> > > + const struct clk_ops *mux_ops;
> > >
> > > mux = kzalloc(sizeof(*mux), GFP_KERNEL);
> > > if (!mux)
> > > @@ -157,10 +215,12 @@ struct clk_hw
> > > *imx8m_clk_hw_composite_flags(const char *name,
> > > div->shift = PCG_DIV_SHIFT;
> > > div->width = PCG_CORE_DIV_WIDTH;
> > > divider_ops = &clk_divider_ops;
> > > + mux_ops = &imx8m_clk_composite_mux_ops;
> > > } else {
> > > div->shift = PCG_PREDIV_SHIFT;
> > > div->width = PCG_PREDIV_WIDTH;
> > > divider_ops = &imx8m_clk_composite_divider_ops;
> > > + mux_ops = &clk_mux_ops;
> > > }
> > >
> > > div->lock = &imx_ccm_lock;
> > > @@ -176,7 +236,7 @@ struct clk_hw
> > *imx8m_clk_hw_composite_flags(const
> > > char *name,
> > > gate->lock = &imx_ccm_lock;
> > >
> > > hw = clk_hw_register_composite(NULL, name, parent_names,
> > > num_parents,
> > > - mux_hw, &clk_mux_ops, div_hw,
> > > + mux_hw, mux_ops, div_hw,
> > > divider_ops, gate_hw, &clk_gate_ops, flags);
> > > if (IS_ERR(hw))
> > > goto fail;
> > > --
> > > 2.16.4
>
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