linux-kernel - Re: [v3,1/4] mfd: cros_ec: Add cros_ec_cmd_xfer

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Date:	Mon, 20 Jun 2016 14:24:32 -0400
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Brian Norris <briannorris@...omium.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Lee Jones <lee.jones@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Olof Johansson <olof@...om.net>, linux-kernel@...r.kernel.org,
	Doug Anderson <dianders@...omium.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Stephen Barber <smbarber@...omium.org>,
	Benson Leung <bleung@...omium.org>,
	Enric Balletbo <enric.balletbo@...labora.co.uk>,
	Randall Spangler <rspangler@...omium.org>,
	Shawn Nematbakhsh <shawnn@...omium.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Todd Broch <tbroch@...omium.org>,
	Gwendal Grignou <gwendal@...omium.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Subject: Re: [v3,1/4] mfd: cros_ec: Add cros_ec_cmd_xfer_status helper

Hello Brian,

On 06/20/2016 02:10 PM, Brian Norris wrote:
> Hi,
> 
> On Mon, Jun 20, 2016 at 10:44:55AM -0700, Brian Norris wrote:
>> On Mon, Jun 20, 2016 at 09:46:57AM -0400, Javier Martinez Canillas wrote:
>>> On 06/18/2016 01:09 PM, Guenter Roeck wrote:
>>>> On 06/17/2016 06:08 PM, Brian Norris wrote:
>>>>> How do you propose we do that? Do all of the following become EINVAL?
>>>>>
>>>
>>> Yes, I would just do that.
>>>
>>> The idea of this helper is to remove duplicated code and AFAICT what most EC
>>> drivers do is something similar to the following:
>>>
>>>         ret = cros_ec_cmd_xfer(ec, msg);
>>>         if (ret < 0)
>>> 	   	return ret;
>>>
>>>         if (msg->result != EC_RES_SUCCESS) {
>>>                 dev_dbg(ec->dev, "EC result %d\n", msg->result);
>>>                 return -EINVAL;
>>>         }
>>>
>>> So in practice what most drivers really care is if the result was successful
>>> or not, I don't see specific EC error handling in the EC drivers.  The real
>>> EC error code is still in the message anyways so drivers that do cares about
>>> the real EC error can look at msg->result instead.
> [...]
>>>>>          EC_RES_INVALID_COMMAND
>>>>
>>>>     -EOPNOTSUPP
>>>>
>>>>>          EC_RES_INVALID_PARAM
>>>>
>>>>     -EINVAL or -EBADMSG
>>>>
>>>>>          EC_RES_INVALID_VERSION
>>>>
>>>>     -EPROTO or -EBADR or -EBADE or -EBADRQC or -EPROTOOPT
>>>>
>>>>>          EC_RES_INVALID_HEADER
>>>>
>>>>     -EPROTO or -EBADR or -EBADE
>>>>
>>>> Doesn't look that bad to me. Also, the raw error could still be logged,
>>>> for example with dev_dbg().
>>>>
>>>
>>> Yes, I think that adding a dev_dbg() with the real EC error code should
>>> be enough, that's basically what drivers do since they can't propagate
>>> the EC error to higher layers anyways.
>>
>> I'll take a look at adding an error code translation table when I get a
>> chance. Hopefully that doesn't delay the others who are planning to use
>> this API shortly...
> 
> Actually, I had some second thoughts, and others brought similar
> concerns up to me:
> 
> What do we really win by doing the translation? It'll be difficult to do
> a 1:1 translation, and any time the EC adds additional error types,
> we'll have to update the translation. What's more, AFAICT, no one will
> really be looking at the translated error codes now, and will just be
> blindly passing them on. So maybe it makes more sense to just pick a
> single error code and pass that on instead. Possibly just -EPROTO (or
> nominate your favorite) for all EC error results, and if someone cares,


I think I didn't make clear in my previous email but yes, I also think
that a translate table for errors is not a good idea and that just a
single -EINVAL (or another error if is more suitable for all EC errors)
will be enough. I say -EINVAL because that's what you first mentioned
in a previous email and that's what most EC clients drivers are using.

I do believe that EC specific errors shouldn't be returned in a Linux
function though for the reasons I explained before.

> they decode msg->result in their driver, or check the dev_dbg() log?
>

And yes, I also think that a dev_dbg() is a good idea (the more data
we have about an error, the better) and as mentioned the EC error can
always be found in the EC message result field.
 
> Brian
> 

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America