linux-kernel - Re: [PATCH v2 3/9] arm: twr-k70f120m: clock driver for Kinetis SoC

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Date:	Tue, 14 Jul 2015 11:03:59 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Paul Osmialowski <pawelo@...g.net.pl>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Jiri Slaby <jslaby@...e.cz>, Kumar Gala <galak@...eaurora.org>,
	Mark Rutland <mark.rutland@....com>,
	Michael Turquette <mturquette@...libre.com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Vinod Koul <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-clk@...r.kernel.org,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	dmaengine@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Paul Bolle <pebolle@...cali.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Uwe Kleine-Koenig <u.kleine-koenig@...gutronix.de>,
	Anson Huang <b20788@...escale.com>,
	Frank Li <Frank.Li@...escale.com>,
	Jingchang Lu <jingchang.lu@...escale.com>,
	Rob Herring <r.herring@...escale.com>,
	Yuri Tikhonov <yur@...raft.com>,
	Sergei Poselenov <sposelenov@...raft.com>,
	Alexander Potashev <aspotashev@...raft.com>
Subject: Re: [PATCH v2 3/9] arm: twr-k70f120m: clock driver for Kinetis SoC

On Tue, Jun 30, 2015 at 2:27 PM, Paul Osmialowski <pawelo@...g.net.pl> wrote:

> Based on K70P256M150SF3RM.pdf K70 Sub-Family Reference Manual, Rev. 3.
>
> Signed-off-by: Paul Osmialowski <pawelo@...g.net.pl>
(...)
> +struct kinetis_sim_regs {
> +       u32 sopt1;      /* System Options Register 1 */
> +       u32 rsv0[1024];
> +       u32 sopt2;      /* System Options Register 2 */
> +       u32 rsv1;
> +       u32 sopt4;      /* System Options Register 4 */
> +       u32 sopt5;      /* System Options Register 5 */
> +       u32 sopt6;      /* System Options Register 6 */
> +       u32 sopt7;      /* System Options Register 7 */
> +       u32 rsv2[2];
> +       u32 sdid;       /* System Device Identification Register */
> +       u32 scgc[KINETIS_SIM_CG_NUMREGS];       /* Clock Gating Regs 1...7 */
> +       u32 clkdiv1;    /* System Clock Divider Register 1 */
> +       u32 clkdiv2;    /* System Clock Divider Register 2 */
> +       u32 fcfg1;      /* Flash Configuration Register 1 */
> +       u32 fcfg2;      /* Flash Configuration Register 2 */
> +       u32 uidh;       /* Unique Identification Register High */
> +       u32 uidmh;      /* Unique Identification Register Mid-High */
> +       u32 uidml;      /* Unique Identification Register Mid Low */
> +       u32 uidl;       /* Unique Identification Register Low */
> +       u32 clkdiv3;    /* System Clock Divider Register 3 */
> +       u32 clkdiv4;    /* System Clock Divider Register 4 */
> +       u32 mcr;        /* Misc Control Register */
> +};

Now there is this design pattern where you copy the datasheet
register map to a struct again.

This is not good if there is a second revision of the hardware and some
registers are shuffled around. IMO it is better to just use #defines
for register
offsets, so you can do exceptions later. Else a new hardware revision
leads to a new struct with new accessor functions etc etc.

Yours,
Linus Walleij
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