linux-kernel - Re: [PATCH V2] clk: meson: vid-pll-div: added meson_vid_pll_div

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Date:   Mon, 20 Mar 2023 16:35:50 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Yu Tu <yu.tu@...ogic.com>
Cc:     linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, kelvin.zhang@...ogic.com,
        qi.duan@...ogic.com
Subject: Re: [PATCH V2] clk: meson: vid-pll-div: added meson_vid_pll_div_ops support

Hello Yu Tu,

On Mon, Mar 20, 2023 at 12:35 PM Yu Tu <yu.tu@...ogic.com> wrote:
>
> Since the previous code only provides "ro_ops" for the vid_pll_div
> clock. In fact, the clock can be set. So add "ops" that can set the
> clock, especially for later chips like S4 SOC and so on.
>
> Signed-off-by: Yu Tu <yu.tu@...ogic.com>
> ---
please describe the changes you did compared to the previous version(s)

[...]
> diff --git a/drivers/clk/meson/vid-pll-div.h b/drivers/clk/meson/vid-pll-div.h
> index c0128e33ccf9..bbccab340910 100644
> --- a/drivers/clk/meson/vid-pll-div.h
> +++ b/drivers/clk/meson/vid-pll-div.h
> @@ -10,11 +10,14 @@
>  #include <linux/clk-provider.h>
>  #include "parm.h"
>
> +#define VID_PLL_DIV_TABLE_SIZE         14
In v1 you used ARRAY_SIZE(vid_pll_div_table) wherever this new macro
is used instead.
I think using ARRAY_SIZE is the better approach because it means the
references will update automatically if an entry is added/removed from
vid_pll_div_table

Also I think there's a different understanding about what Jerome
previously wrote:
> It would be nice to actually describe how this vid pll work so we can
> stop using precompute "magic" values and actually use the IP to its full
> capacity.
>From what I understand is that you interpreted this as "let's change
ARRAY_SIZE(vid_pll_div_table) to a new macro called
VID_PLL_DIV_TABLE_SIZE".
But I think what Jerome meant is: "let's get rid of vid_pll_div_table
and implement how to actually calculate the clock rate - without
hard-coding 14 possible clock settings in vid_pll_div_table". Look at
clk-mpll.c and/or clk-pll.c which allow calculating arbitrary rates
without any hard-coded tables.


Best regards,
Martin