linux-kernel - Re: [PATCH v2 17/17] power: supply: olpc

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Date:   Sun, 2 Dec 2018 15:34:58 -0800
From:   Darren Hart <dvhart@...radead.org>
To:     Lubomir Rintel <lkundrak@...sk>
Cc:     Mark Brown <broonie@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Andy Shevchenko <andy@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        James Cameron <quozl@...top.org>,
        Sebastian Reichel <sre@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Eric Miao <eric.y.miao@...il.com>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Daniel Mack <daniel@...que.org>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        platform-driver-x86@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 17/17] power: supply: olpc_battery: Add OLPC XO 1.75
 support

On Fri, Nov 16, 2018 at 05:24:03PM +0100, Lubomir Rintel wrote:
> The battery and the protocol are essentially the same as OLPC XO 1.5,
> but the responses from the EC are LSB first.
> 
> Signed-off-by: Lubomir Rintel <lkundrak@...sk>
> Acked-by: Pavel Machek <pavel@....cz>
> 
> ---
> Changes since v1:
> - s/s16 ecword_to_cpu/u16 ecword_to_cpu/
> - s/u16 ec_byte/u16 ec_word/
> 
>  drivers/power/supply/olpc_battery.c | 23 ++++++++++++++++++-----
>  1 file changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/power/supply/olpc_battery.c b/drivers/power/supply/olpc_battery.c

...

> @@ -626,6 +635,10 @@ static int olpc_battery_probe(struct platform_device *pdev)
>  	if (ecver > 0x44) {
>  		/* XO 1 or 1.5 with a new EC firmware. */
>  		data->new_proto = 1;
> +	} else if (of_find_compatible_node(NULL, NULL, "olpc,xo1.75-ec")) {

This if/else blocks concerns me a bit, but I might just be missing some
context.

This tests both ecver as well as the OF compatible string, is this reliable? Do
we know that for all xo1.75-ec compatible nodes the ecver will be <= 0x44? Or,
is ecver undefined? If the latter, then perhaps this test should be performed
first?

if (of_find_compatible_node....x01.75-ec...)
	...
else if (ecver > 0x44)
	...
else
	...

And what happens when ecver == 0x44? We test for > and < but not ==, <=,
or >= in this block

> +		/* XO 1.75 */
> +		data->new_proto = 1;
> +		data->little_endian = 1;
>  	} else if (ecver < 0x44) {
>  		/*
>  		 * We've seen a number of EC protocol changes; this driver
> -- 
> 2.19.1
> 
> 

-- 
Darren Hart
VMware Open Source Technology Center