Re: [PATCH] i2c: aspeed: Improve driver to support multi-master use cases stably

From: Brendan Higgins <brendanhiggins@google.com>
To: jae.hyun.yoo@linux.intel.com
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Joel Stanley <joel@jms.id.au>,  Andrew Jeffery <andrew@aj.id.au>,
	linux-i2c@vger.kernel.org,
	 OpenBMC Maillist <openbmc@lists.ozlabs.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 linux-aspeed@lists.ozlabs.org,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	james.feist@linux.intel.com,  vernon.mauery@linux.intel.com,
	Benjamin Fair <benjaminfair@google.com>,
	 Patrick Venture <venture@google.com>,
	gary_hsu@aspeedtech.com,  Ryan Chen <ryan_chen@aspeedtech.com>
Subject: Re: [PATCH] i2c: aspeed: Improve driver to support multi-master use cases stably
Date: Fri, 13 Jul 2018 11:12:55 -0700	[thread overview]
Message-ID: <CAFd5g47zdPdqqjVJtNHtFk+jKgciKbMcEH9M-W9rL4DgLM5hkg@mail.gmail.com> (raw)
In-Reply-To: <d3f10fc1-635b-3a5d-a967-2816eac005fc@linux.intel.com>

On Fri, Jul 13, 2018 at 10:22 AM Jae Hyun Yoo
<jae.hyun.yoo@linux.intel.com> wrote:
>
> On 7/12/2018 11:21 AM, Jae Hyun Yoo wrote:
> > On 7/12/2018 2:33 AM, Brendan Higgins wrote:
> >> On Wed, Jun 27, 2018 at 10:55 AM Jae Hyun Yoo
> >> <jae.hyun.yoo@linux.intel.com> wrote:
<snip>
> >> <snip>
> >>>>> +       for (;;) {
> >>>>> +               if (!(readl(bus->base + ASPEED_I2C_CMD_REG) &
> >>>>> +                     (ASPEED_I2CD_BUS_BUSY_STS |
> >>>>> +                      ASPEED_I2CD_XFER_MODE_STS_MASK)))
> >>>>
> >>>> Is using the Transfer Mode State Machine bits necessary? The
> >>>> documentation marks it as "for debugging purpose only," so relying on
> >>>> it makes me nervous.
> >>>>
> >>>
> >>> As you said, the documentation marks it as "for debugging purpose only."
> >>> but ASPEED also uses this way in their SDK code because it's the best
> >>> way for checking bus busy status which can cover both single and
> >>> multi-master use cases.
> >>>
> >>
> >> Well, it would also be really nice to have access to this bit if
> >> someone wants
> >> to implement MCTP. Could we maybe check with Aspeed what them meant by
> >> "for
> >> debugging purposes only" and document it here? It makes me nervous to
> >> rely on
> >> debugging functionality for normal usage.
> >>
> >
> > Okay, I'll check it with Aspeed. Will let you know their response.
> >
>
> I've checked it with Gary Hsu <gary_hsu@aspeedtech.com> and he confirmed
> that the bits reflect real information and good to be used in practical
> code.

Huh. For my own edification, could you ask them why they said "for debugging
purpose only" in the documentation? I am just really curious what they meant by
that. I would be satisfied if you just CC'ed me on your email thread with Gary,
and I can ask him myself.

>
> I'll add a comment like below:
>
> /*
>   * This is marked as 'for debugging purpose only' in datasheet but
>   * ASPEED confirmed that this reflects real information and good
>   * to be used in practical code.
>   */
>
> Is it acceptable then?

Yeah, that's fine.

<snip>

Cheers