linux-kernel - Re: [PATCH] clocksource: sh_cmt: use CMTOUT

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Date:   Mon, 8 Mar 2021 09:35:31 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Phong Hoang <phong.hoang.wz@...esas.com>
Cc:     Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Niklas Söderlund <niklas.soderlund@...natech.se>
Subject: Re: [PATCH] clocksource: sh_cmt: use CMTOUT_IE only when supported

Hi Wolfram, Phong-san,

On Fri, Mar 5, 2021 at 2:30 PM Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
> CMTOUT_IE is only supported for older SoCs. Newer SoCs shall not set
> this bit. So, add a version check.
>
> Reported-by: Phong Hoang <phong.hoang.wz@...esas.com>
> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>

Thanks for your patch!

As R-Car Gen2/3 indeed don't have this bit:
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>

But given my comments below, I think it would make sense to change the
one-line summary to e.g. "clocksource: sh_cmt: R-Car Gen2/Gen3 do not
have CMTOUT_IE".

> --- a/drivers/clocksource/sh_cmt.c
> +++ b/drivers/clocksource/sh_cmt.c
> @@ -143,6 +143,7 @@ struct sh_cmt_device {
>  #define SH_CMT32_CMCSR_SSIE            (1 << 10)
>  #define SH_CMT32_CMCSR_CMS             (1 << 9)
>  #define SH_CMT32_CMCSR_CMM             (1 << 8)
> +/* CMTOUT_IE only for SH_CMT_32BIT and SH_CMT_48BIT */
>  #define SH_CMT32_CMCSR_CMTOUT_IE       (1 << 7)
>  #define SH_CMT32_CMCSR_CMR_NONE                (0 << 4)
>  #define SH_CMT32_CMCSR_CMR_DMA         (1 << 4)
> @@ -339,8 +340,9 @@ static int sh_cmt_enable(struct sh_cmt_channel *ch)
>                 sh_cmt_write_cmcsr(ch, SH_CMT16_CMCSR_CMIE |
>                                    SH_CMT16_CMCSR_CKS512);
>         } else {
> -               sh_cmt_write_cmcsr(ch, SH_CMT32_CMCSR_CMM |
> -                                  SH_CMT32_CMCSR_CMTOUT_IE |
> +               u32 cmtout = ch->cmt->info->model <= SH_CMT_48BIT ?
> +                             SH_CMT32_CMCSR_CMTOUT_IE : 0;
> +               sh_cmt_write_cmcsr(ch, cmtout | SH_CMT32_CMCSR_CMM |
>                                    SH_CMT32_CMCSR_CMR_IRQ |
>                                    SH_CMT32_CMCSR_CKS_RCLK8);
>         }

Note that this bit is still set for all "32-bit" and all other "48-bit"
variants:

SH_CMT_32BIT:
sh7720: CMTOUT_IE supported
sh7343/7366: no docs
sh7722/sh7723: limited docs, but "Supports canceling of the standby
state in U-standby mode."
sh7724: CMTOUT_IE supported

SH_CMT_48BIT:
sh73a0/r8a7740: CMTOUT_IE supported on channels 1/2/3, not on 0/4/5

So even not all older models support this bit.
Probably this bit should only be set when the timer is configured as a
wake-up source.  But that is out-of-scope for this patch.

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