linux-kernel - Re: [PATCH v2] platform: cros_ec: Reduce ligthbar get version command

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Date:   Sun, 30 Aug 2020 00:00:02 -0700
From:   Gwendal Grignou <gwendal@...omium.org>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-iio <linux-iio@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] platform: cros_ec: Reduce ligthbar get version command

On Sat, Aug 29, 2020 at 8:54 AM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Tue, 25 Aug 2020 17:29:45 -0700
> Gwendal Grignou <gwendal@...omium.org> wrote:
>
> > By default, the lightbar commands are set to the
> > biggest lightbar command and response. That length is greater than 128
> > bytes and may not work on all machines.
> > But all EC are probed for lightbar by sending a get version request.
> > Set that request size precisely.
> >
> > Before the command would be:
> > cros_ec_cmd: version: 0, command: EC_CMD_LIGHTBAR_CMD, outsize: 194, insize: 128, result: 0
> > Afer:
> > cros_ec_cmd: version: 0, command: EC_CMD_LIGHTBAR_CMD, outsize: 1, insize: 8, result: 0
> >
> > Signed-off-by: Gwendal Grignou <gwendal@...omium.org>
> Hi Gwendal,
>
> Description seems to me to suggest this is a fix?
> Are there known machines on which it doesn't work currently?
We have a prototype [without lightbar] where the command size was
limited to 128 bytes.
Given we issue a get_lightbar_version on all chromebooks, we had a
failure on this prototype. Devices with a lightbar must support a
command size greater or equal to 194 bytes.
Beside helping the prototype to boot, this patch slightly speeds up
the enumeration of devices managed by the EC.
>
> If so, please can I have a fixes tag.  If it's just a precaution
> against future problems then let me know and I can add it for the
> next merge window.
Done in v3.
Note I made a mistake by sending the patch to linux-iio as it targeted
platform/chromeos.
>
> Thanks,
>
> Jonathan
>
> > ---
> > Changes since v1:
> > - Remove BUG and TEST fields.
> >
> >  drivers/platform/chrome/cros_ec_lightbar.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/platform/chrome/cros_ec_lightbar.c b/drivers/platform/chrome/cros_ec_lightbar.c
> > index b59180bff5a3e..ef61298c30bdd 100644
> > --- a/drivers/platform/chrome/cros_ec_lightbar.c
> > +++ b/drivers/platform/chrome/cros_ec_lightbar.c
> > @@ -116,6 +116,8 @@ static int get_lightbar_version(struct cros_ec_dev *ec,
> >
> >       param = (struct ec_params_lightbar *)msg->data;
> >       param->cmd = LIGHTBAR_CMD_VERSION;
> > +     msg->outsize = sizeof(param->cmd);
> > +     msg->result = sizeof(resp->version);
> >       ret = cros_ec_cmd_xfer_status(ec->ec_dev, msg);
> >       if (ret < 0) {
> >               ret = 0;
>