linux-kernel - Re: [PATCH v2 4/4] media: rcar-csi2: Add D-PHY support for V4H

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Message-ID: <CAMuHMdUbMRBFV-7hDMQ3-UKAhzfbGM5yZJz05aGAHpOKZ5eKcQ@mail.gmail.com>
Date: Mon, 12 May 2025 09:37:48 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
Cc: ALOK TIWARI <alok.a.tiwari@...cle.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>, 
	Laurent Pinchart <laurent.pinchart@...asonboard.com>, linux-media@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] media: rcar-csi2: Add D-PHY support for V4H

Hi Niklas,

On Sun, 11 May 2025 at 22:03, Niklas Söderlund
<niklas.soderlund+renesas@...natech.se> wrote:
> On 2025-05-12 00:37:09 +0530, ALOK TIWARI wrote:
> > On 11-05-2025 23:17, Niklas Söderlund wrote:
> > > +   rcsi2_write16(priv, V4H_CORE_DIG_COMMON_RW_DESKEW_FINE_MEM_REG, 0x0404);
> > > +   rcsi2_write16(priv, V4H_CORE_DIG_COMMON_RW_DESKEW_FINE_MEM_REG, 0x040c);
> > > +   rcsi2_write16(priv, V4H_CORE_DIG_COMMON_RW_DESKEW_FINE_MEM_REG, 0x0414);
> > > +   rcsi2_write16(priv, V4H_CORE_DIG_COMMON_RW_DESKEW_FINE_MEM_REG, 0x041c);

 [...]

> > Instead of manually writing each call, it could use a loop ?
> >
> > for (int i = 0x0404; i <= 0x07fc; i += 0x08) {
> >     rcsi2_write16(priv, V4H_CORE_DIG_COMMON_RW_DESKEW_FINE_MEM_REG, i);
>
> Unfortunately the values are not all sequential, see the progression
> 0x061c -> 0x0623 and 0x071c -> 0x0723 for example.
>
> > or if values are not strictly sequential, iterating over the array.
> > static const u16 register_values[]= {0x0404, 0x040c, 0x0414 etc,,}
> > rcsi2_write16(priv, V4H_CORE_DIG_COMMON_RW_DESKEW_FINE_MEM_REG,
> > register_values[i]);
>
> I agree with you, a array of values would make this look a tad less
> silly and would reduce the number of lines. I considered this while
> writing it but opted for this. My reason was as most of the register
> writes needed to setup the PHY are not documented in the docs I have and
> I wanted to keep the driver as close to the table of magic values I have
> to make it easy to compare driver and the limited documentation.
>
> I guess it's really a matter of style. I have no real strong opinion, if
> people think an array would be nicer I have no issue switching to that.

Have you looked at the impact on kernel size?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds