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

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Date:   Fri, 13 Jul 2018 11:12:55 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     jae.hyun.yoo@...ux.intel.com
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>, linux-i2c@...r.kernel.org,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-aspeed@...ts.ozlabs.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        james.feist@...ux.intel.com, vernon.mauery@...ux.intel.com,
        Benjamin Fair <benjaminfair@...gle.com>,
        Patrick Venture <venture@...gle.com>, gary_hsu@...eedtech.com,
        Ryan Chen <ryan_chen@...eedtech.com>
Subject: Re: [PATCH] i2c: aspeed: Improve driver to support multi-master use
 cases stably

On Fri, Jul 13, 2018 at 10:22 AM Jae Hyun Yoo
<jae.hyun.yoo@...ux.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@...ux.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@...eedtech.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