linux-kernel - Re: [PATCH v2] drivers/misc: (aspeed-lpc-snoop): Add ast2400 to compat

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Date:   Wed, 5 Jul 2017 21:43:23 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Patrick Venture <venture@...gle.com>
Cc:     Joel Stanley <joel@....id.au>, Robert Lippert <roblip@...il.com>,
        gregkh <gregkh@...uxfoundation.org>,
        Rick Altherr <raltherr@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drivers/misc: (aspeed-lpc-snoop): Add ast2400 to compat

On Wed, Jul 5, 2017 at 9:04 PM, Patrick Venture <venture@...gle.com> wrote:
> This driver can be used on the aspeed ast2400 with minor
> modifications.
>
> Tested: ast2400 on quanta-q71l
>
> Signed-off-by: Patrick Venture <venture@...gle.com>
> ---
> v2: added aspeed-g5 area because ast2400 doesn't use those bits.
>     also updated commit message.
> ---
>  drivers/misc/aspeed-lpc-snoop.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/misc/aspeed-lpc-snoop.c b/drivers/misc/aspeed-lpc-snoop.c
> index 593905565b74..83f9a9e5a7cf 100644
> --- a/drivers/misc/aspeed-lpc-snoop.c
> +++ b/drivers/misc/aspeed-lpc-snoop.c
> @@ -155,8 +155,9 @@ static int aspeed_lpc_enable_snoop(struct aspeed_lpc_snoop *lpc_snoop,
>         regmap_update_bits(lpc_snoop->regmap, HICR5, hicr5_en, hicr5_en);
>         regmap_update_bits(lpc_snoop->regmap, SNPWADR, snpwadr_mask,
>                            lpc_port << snpwadr_shift);
> +#ifdef CONFIG_MACH_ASPEED_G5
>         regmap_update_bits(lpc_snoop->regmap, HICRB, hicrb_en, hicrb_en);
> -
> +#endif
>         return rc;
>  }

Hi Patrick,

Sorry for bringing up yet another point on a fairly trivial patch, but
in general,
I'd recommend making this a runtime check rather than compile-time.

At the moment, your version is safe because CONFIG_MACH_ASPEED_G5
and CONFIG_MACH_ASPEED_G4 are mutually exclusive and there is
always one of them set, but once we get support for G6, G7 etc,
the driver might silently break when it behaves differently depending
on a configuration option that may or may not be set on a particular
kernel build.

You can use the .data field in the of_device_id to add a trigger for the
behavior change.

       Arnd