linux-kernel - Re: [PATCH 1/2] power: supply: sbs-battery: don't assume MANUFACTURER

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Message-ID: <20180706112854.nj762elcad625idr@earth.universe>
Date:   Fri, 6 Jul 2018 13:28:54 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.co.uk>
To:     Brian Norris <briannorris@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        Rhyland Klein <rklein@...dia.com>,
        Alexandru Stan <amstan@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Doug Anderson <dianders@...omium.org>,
        Phil Reid <preid@...ctromag.com.au>
Subject: Re: [PATCH 1/2] power: supply: sbs-battery: don't assume
 MANUFACTURER_DATA formats

Hi,

On Tue, Jun 12, 2018 at 01:20:41PM -0700, Brian Norris wrote:
> This driver was originally submitted for the TI BQ20Z75 battery IC
> (commit a7640bfa10c5 ("power_supply: Add driver for TI BQ20Z75 gas gauge
> IC")) and later renamed to express generic SBS support. While it's
> mostly true that this driver implemented a standard SBS command set, it
> takes liberties with the REG_MANUFACTURER_DATA register. This register
> is specified in the SBS spec, but it doesn't make any mention of what
> its actual contents are.
> 
> We've sort of noticed this optionality previously, with commit
> 17c6d3979e5b ("sbs-battery: make writes to ManufacturerAccess
> optional"), where we found that some batteries NAK writes to this
> register.
> 
> What this really means is that so far, we've just been lucky that most
> batteries have either been compatible with the TI chip, or else at least
> haven't reported highly-unexpected values.
> 
> For instance, one battery I have here seems to report either 0x0000 or
> 0x0100 to the MANUFACTURER_ACCESS_STATUS command -- while this seems to
> match either Wake Up (bits[11:8] = 0000b) or Normal Discharge
> (bits[11:8] = 0001b) status for the TI part [1], they don't seem to
> actually correspond to real states (for instance, I never see 0101b =
> Charge, even when charging).
> 
> On other batteries, I'm getting apparently random data in return, which
> means that occasionally, we interpret this as "battery not present" or
> "battery is not healthy".
> 
> All in all, it seems to be a really bad idea to make assumptions about
> REG_MANUFACTURER_DATA, unless we already know what battery we're using.
> Therefore, this patch reimplements the "present" and "health" checks to
> the following on most SBS batteries:
> 
> 1. HEALTH: report "unknown" -- I couldn't find a standard SBS command
>    that gives us much useful here
> 2. PRESENT: just send a REG_STATUS command; if it succeeds, then the
>    battery is present
> 
> Also, we stop sending MANUFACTURER_ACCESS_SLEEP to non-TI parts. I have
> no proof that this is useful and supported.
> 
> If someone explicitly provided a 'ti,bq20z75' compatible property, then
> we continue to use the existing TI command behaviors, and we effectively
> revert commit 17c6d3979e5b ("sbs-battery: make writes to
> ManufacturerAccess optional") to again make these commands required.
> 
> [1] http://www.ti.com/lit/er/sluu265a/sluu265a.pdf
> 
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> Reviewed-by: Guenter Roeck <linux@...ck-us.net>
> Acked-by: Rhyland Klein <rklein@...dia.com>
> ---

Thanks, queued to power-supply-next.

-- Sebastian

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