linux-kernel - Re: [linux-sunxi] Re: [PATCH v6 1/6] clk: sunxi-ng: div: Add support for fixed post-divider

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Date:   Sat, 12 Aug 2017 12:13:38 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Priit Laes <plaes@...es.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Jonathan Liu <net147@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [linux-sunxi] Re: [PATCH v6 1/6] clk: sunxi-ng: div: Add support
 for fixed post-divider

On Sat, Aug 12, 2017 at 11:07 AM,  <icenowy@...c.io> wrote:
> 在 2017-07-17 16:52，Maxime Ripard 写道：
>>
>> On Fri, Jul 14, 2017 at 05:49:23PM +0300, Priit Laes wrote:
>>>
>>> SATA clock on sun4i/sun7i is of type (parent) / M / 6 where
>>> 6 is fixed post-divider.
>>>
>>> Signed-off-by: Priit Laes <plaes@...es.org>
>>> ---
>>>  drivers/clk/sunxi-ng/ccu_div.c | 15 +++++++++++++--
>>>  drivers/clk/sunxi-ng/ccu_div.h |  3 ++-
>>>  2 files changed, 15 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/clk/sunxi-ng/ccu_div.c
>>> b/drivers/clk/sunxi-ng/ccu_div.c
>>> index c0e5c10..744502a 100644
>>> --- a/drivers/clk/sunxi-ng/ccu_div.c
>>> +++ b/drivers/clk/sunxi-ng/ccu_div.c
>>> @@ -21,6 +21,9 @@ static unsigned long ccu_div_round_rate(struct
>>> ccu_mux_internal *mux,
>>>  {
>>>         struct ccu_div *cd = data;
>>>
>>> +       if (cd->common.features & CCU_FEATURE_FIXED_POSTDIV)
>>> +               rate *= cd->fixed_post_div;
>>> +
>>>         return divider_round_rate_parent(&cd->common.hw, parent,
>>>                                          rate, parent_rate,
>>>                                          cd->div.table, cd->div.width,
>>
>>
>>
>> You still haven't addressed the biggest issue with this patch, see:
>> https://patchwork.kernel.org/patch/9825565/
>
>
> I think he has already did the changes suggested in the review.

Nope. Only half of it is fixed. First you "unapply" the post-divider,
i.e. multiply the rate by the divider. Then you pass it to
divider_round_rate_parent. You still have to reapply the divider
to the result. This last part is missing. This means the clock
rate returned by ccu_div_round_rate is going to be off.

Instead the return statement should be

    return divider_round_rate_parent(...) / cd->fixed_post_div

ChenYu

>
> (P.S. during developing R40 CCU driver I found that pll-periph0-sata
> also needs this patch, so I'm rechecking it)
>
>>
>> Maxime
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
>
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