linux-kernel - Re: [PATCH v2 3/3] spi: meson-axg: add a linear clock divider support

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Date:   Thu, 13 Dec 2018 22:37:07 +0800
From:   Sunny Luo <sunny.luo@...ogic.com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Mark Brown <broonie@...nel.org>
CC:     Yixun Lan <yixun.lan@...ogic.com>,
        Kevin Hilman <khilman@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        Xingyu Chen <xingyu.chen@...ogic.com>,
        <linux-spi@...r.kernel.org>, <linux-amlogic@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] spi: meson-axg: add a linear clock divider support

Hi Jerome,

On 2018/12/13 17:28, Jerome Brunet wrote:
> On Thu, 2018-12-13 at 09:55 +0100, Neil Armstrong wrote:

>>> diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
>>>   config SPI_MESON_SPICC
>>>   	tristate "Amlogic Meson SPICC controller"
>>> -	depends on ARCH_MESON || COMPILE_TEST
>>> +	depends on OF && COMMON_CLK && (ARCH_MESON || COMPILE_TEST)
> 
> The purpose of this patch is clock, right ? Why does it add a dependency on OF
> ?
> I did it by the way. Maybe it's better to add it in patch 1.


>>> +static int meson_spicc_clk_init(struct meson_spicc_device *spicc)
>>> +{
>>> +	struct device *dev = &spicc->pdev->dev;
>>> +	struct clk_fixed_factor *div0;
>>> +	struct clk_divider *div1;
> 
> Could you come up with something better than div0 and div1 ? it is confusing,
> especially with the comment above about div3 and 4 ... fixed_factor, div maybe
> ?
> Good, It is really confusing, I will change next patch.


>>> +	div1 = &meson_spicc_div1;
>>> +	div1->reg = spicc->base + (u64)div1->reg;
> 
> So you have static data which you override here. This works only if there is a
> single instance ... and does not really improve readability in your case.
> 
> IMO, you'd be better off without the static data above.

This is a terrible bug for more than one instances. I must overwrite it.


>>> +	if (!spicc->data->has_enhance_clk_div) {
> 
> Do all SoC with 'has_oen' have 'has_enhance_clk_div' too ?
> DO you really need two flags ?

Yes, all Soc with 'has_oen' must have 'has_enhance_clk_div' too.
It is distinct to use two flags here, what do you think of it?

>>> +	mux = &meson_spicc_sel;
>>> +	snprintf(name, sizeof(name), "%s#_sel", dev_name(dev));
>>> +	init.name = name;
>>> +	init.ops = &clk_mux_ops;
>>> +	init.parent_names = mux_parent_names;
>>> +	init.num_parents = 2;
>>> +	init.flags = CLK_SET_RATE_PARENT | CLK_SET_RATE_NO_REPARENT;
> 
> Why CLK_SET_RATE_NO_REPARENT ? CCF should pick the parent that give the best
> results, best to let it do its task ...
> 
There are two div in AXG, one is the coarse old-div and the other is 
enhance-div. From SoCs designer's opinion, the ehance-div aims to take 
place of the old-div.