Re: [PATCH] applesmc: Re-work SMC comms v2

From: Henrik Rydberg <rydberg@bitmath.org>
To: Brad Campbell <brad@fnarfbargle.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
	linux-hwmon@vger.kernel.org,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	hns@goldelico.com, Guenter Roeck <linux@roeck-us.net>,
	Andreas Kemnade <andreas@kemnade.info>,
	Jean Delvare <jdelvare@suse.com>
Subject: Re: [PATCH] applesmc: Re-work SMC comms v2
Date: Sun, 8 Nov 2020 09:22:14 +0100	[thread overview]
Message-ID: <bddf0050-4189-4ca4-8077-71683bcc4b10@bitmath.org> (raw)
In-Reply-To: <26d3f4f5-2e9a-cd20-1531-74cf44ef738c@fnarfbargle.com>

Hi Brad,

> G'day Henrik,
> 
> Which kernel was this based on? It won't apply to my 5.9 tree.

I was being lazy and applied the diff to linus/master on top of my 
current stable branch. More importantly, I sent the mail out from an 
email client that may not format the patch properly; I'll fix that.

> I assume the sprinkling of udelay(APPLESMC_MIN_WAIT) means the SMC is
> slow in getting its status register set up. Could we instead just put
> a single one of those up-front in wait_status?

That works fine, just a matter of taste.

> Any chance you could try this one? I've added a retry to send_command and
> added a single global APPLESMC_MIN_WAIT before each status read.
> 
>  From looking at your modified send_command, it appears the trigger for a
> retry is sending a command and the SMC doing absolutely nothing. This
> should do the same thing.

Not quite, unfortunately. The patch that works waits for a drop of 
IB_CLOSED, then checks the BUSY status. If not seen, it resends 
immediately, never expecting to see it. The patch in this email creates 
a dreadfully sluggish probe, and the occasional failure.

> Interestingly enough, by adding the udelay to wait_status on my machine I've
> gone from 24 reads/s to 50 reads/s.

Yep, I experience the same positive effect.

> I've left out the remainder of the cleanups. Once we get a minimally working
> patch I was going to look at a few cleanups, and I have some patches pending
> to allow writing to the SMC from userspace (for setting BCLM and BFCL mainly)

All fine. I will respond to the v3 mail separately.

Henrik