linux-kernel - Re: [PATCH v4 4/5] clk: hi6220: Clock driver support for Hisilicon hi6220 SoC

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Message-ID: <20150515193041.GO31753@codeaurora.org>
Date:	Fri, 15 May 2015 12:30:41 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Bintian <bintian.wang@...wei.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	catalin.marinas@....com, will.deacon@....com,
	devicetree@...r.kernel.org, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, khilman@...aro.org, mturquette@...aro.org,
	rob.herring@...aro.org, zhangfei.gao@...aro.org,
	haojian.zhuang@...aro.org, xuwei5@...ilicon.com,
	jh80.chung@...sung.com, olof@...om.net, yanhaifeng@...il.com,
	xuejiancheng@...wei.com, sledge.yanwei@...wei.com,
	tomeu.vizoso@...labora.com, linux@....linux.org.uk,
	guodong.xu@...aro.org, jorge.ramirez-ortiz@...aro.org,
	tyler.baker@...aro.org, khilman@...nel.org, pebolle@...cali.nl,
	arnd@...db.de, marc.zyngier@....com, xuyiping@...ilicon.com,
	wangbinghui@...ilicon.com, zhenwei.wang@...ilicon.com,
	victor.lixin@...ilicon.com, puck.chen@...ilicon.com,
	dan.zhao@...ilicon.com, huxinwei@...wei.com,
	z.liuxinliang@...wei.com, heyunlei@...wei.com,
	kong.kongxinwei@...ilicon.com, btw@...l.itp.ac.cn, w.f@...wei.com,
	liguozhu@...ilicon.com
Subject: Re: [PATCH v4 4/5] clk: hi6220: Clock driver support for Hisilicon
 hi6220 SoC

On 05/15, Bintian wrote:
> On 2015/5/15 8:25, Stephen Boyd wrote:
> >On 05/05, Bintian Wang wrote:
> >>diff --git a/drivers/clk/hisilicon/clkdivider-hi6220.c b/drivers/clk/hisilicon/clkdivider-hi6220.c
> >>+
> >>+/**
> >>+ * struct hi6220_clk_divider - divider clock for hi6220
> >>+ *
> >>+ * @hw:		handle between common and hardware-specific interfaces
> >>+ * @reg:	register containing divider
> >>+ * @shift:	shift to the divider bit field
> >>+ * @width:	width of the divider bit field
> >>+ * @mask:	mask for setting divider rate
> >>+ * @table:	the div table that the divider supports
> >>+ * @lock:	register lock
> >>+ */
> >>+struct hi6220_clk_divider {
> >>+	struct clk_hw	hw;
> >>+	void __iomem	*reg;
> >>+	u8		shift;
> >>+	u8		width;
> >>+	u32		mask;
> >>+	const struct clk_div_table *table;
> >>+	spinlock_t	*lock;
> >>+};
> >
> >The clk-divider.c code has been made "reusable". Can you please
> >try to use the functions that it now exposes instead of
> >copy/pasting it and modifying it to suit your needs? A lot of
> >this code looks the same.
> In fact, I discussed this problem with Rob Herring and Mike Turquette
> in the 96boards internal mail list before.
> 
> The divider in hi6220 has a mask bit to guarantee writing the correct
> bits in register when setting rate, but the index of this mask bit has
> no rules to get (e.g. by left shift some fixed bits), so I add this
> divider clock to handle it, we can regard hi6220_clk_divider as a
> special case of generic divider clock.
> 
> If I don't add this divider clock for hi6220 chip, then I should change
> the core APIs "clk_register_divider" and "clk_register_divider_table",
> and then many other drivers will be updated.
> So I think just add this divider clock is a good solution now.

I think you missed my point. I didn't suggest using
clk_register_divider or clk_register_divider_table(). I'm
suggesting to use 

unsigned long divider_recalc_rate(struct clk_hw *hw, unsigned long parent_rate,
                unsigned int val, const struct clk_div_table *table,
                unsigned long flags);
long divider_round_rate(struct clk_hw *hw, unsigned long rate,
                unsigned long *prate, const struct clk_div_table *table,
                u8 width, unsigned long flags);
int divider_get_val(unsigned long rate, unsigned long parent_rate,
                const struct clk_div_table *table, u8 width,
                unsigned long flags);

> >>+		return ERR_PTR(-ENOMEM);
> >>+	}
> >>+
> >>+	for (i = 0; i < max_div; i++) {
> >>+		table[i].div = min_div + i;
> >>+		table[i].val = table[i].div - 1;
> >>+	}
> >>+
> >>+	init.name = name;
> >>+	init.ops = &hi6220_clkdiv_ops;
> >>+	init.flags = flags | CLK_IS_BASIC;
> >
> >It's basic?
> I rechecked this flag, it's really useless to us, so I can remove it.
> But can you tell me which case I should use it?

I think the basic flag is there for drivers that want to know what type
of clock they're dealing with when all they have is the struct clk_hw
pointer. I like to discourage use of this flag in hopes of deleting
it someday.

> 
> How about just send this patch for review not the whole patch set in
> next version?
> 

Yes a single patch is fine. I take it you want the patch to go
through arm-soc with some Ack from us?

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