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From: Brendan Higgins <brendanhiggins@google.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "Wolfram Sang" <wsa@the-dreams.de>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Jason Cooper" <jason@lakedaemon.net>,
	"Marc Zyngier" <marc.zyngier@arm.com>,
	"Joel Stanley" <joel@jms.id.au>,
	"Vladimir Zapolskiy" <vz@mleia.com>,
	"Kachalov Anton" <mouse@mayc.ru>,
	"Cédric Le Goater" <clg@kaod.org>,
	linux-i2c@vger.kernel.org, devicetree@vger.kernel.org,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"OpenBMC Maillist" <openbmc@lists.ozlabs.org>
Subject: Re: [PATCH v6 1/5] irqchip/aspeed-i2c-ic: binding docs for Aspeed I2C Interrupt Controller
Date: Wed, 29 Mar 2017 13:51:57 -0700	[thread overview]
Message-ID: <CAFd5g460U4c3rMtKphxnu=OADTfD=oe8Z+JPn-H82zpHKJUqfw@mail.gmail.com> (raw)
In-Reply-To: <1490789505.3177.184.camel@kernel.crashing.org>

> Regarding the other comment about the "fast mode", my main worry here
> is that somebody might come up with a 2Mhz capable device, we'll hit
> your 1Mhz test, enable fast mode, and shoot it with 3.4Mhz which it
> might not be happy at all about...
>
> I think the cut-off for switching to the "fast" mode should basically
> be the fast speed mode frequency (which isn't clear from the spec but
> seems to be 3.4Mhz). Otherwise people will end up with higher speeds
> than what they asked for and that's bad.

Ah, but see the documentation only says that high speed mode sets the
Base Clock divisor to zero; is does not say anything about tCKHigh or
tCKLow (clk_high and clk_low in my code respectively), which are the
only parameters which are manipulated for speeds greater than or equal
to 1.5MHz since:

# I forgot the "APB_freq /" part in the comment on my
aspeed_i2c_get_clk_reg_val(...)
# My function still does the computation correctly, I just forgot this
in the comment.
SCL_freq = APB_freq / (1 << base_clk) * (clk_high + 1 + clk_low + 1)

so if base_clk = 0, clk_high = 15, clk_low = 15, APB_freq = 50MHz

SCL_freq = APB_freq / (1 << base_clk) * (clk_high + 1 + clk_low + 1)
                = 50000000 / (1 << 0) * (15 + 1 + 15 + 1)
                = 50000000 / 32
                = 1562500Hz
                = ~1.5MHz

so maybe instead of setting a hard limit like I did, maybe the best
thing is to just check and see what the base_clk gets set to and if it
gets set to zero, we turn on high speed mode. What do you think?

Cheers

  reply	other threads:[~2017-03-29 20:52 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-28  5:12 [PATCH v6 0/5] i2c: aspeed: added driver for Aspeed I2C Brendan Higgins
2017-03-28  5:12 ` [PATCH v6 1/5] irqchip/aspeed-i2c-ic: binding docs for Aspeed I2C Interrupt Controller Brendan Higgins
2017-03-28  8:49   ` Benjamin Herrenschmidt
2017-03-29 10:34     ` Brendan Higgins
2017-03-29 12:11       ` Benjamin Herrenschmidt
2017-03-29 20:51         ` Brendan Higgins [this message]
2017-03-29 21:17           ` Benjamin Herrenschmidt
2017-04-03 14:16   ` Rob Herring
2017-03-28  5:12 ` [PATCH v6 2/5] irqchip/aspeed-i2c-ic: Add I2C IRQ controller for Aspeed Brendan Higgins
2017-03-28  8:32   ` Marc Zyngier
2017-03-28  9:12     ` Benjamin Herrenschmidt
2017-03-28  9:40       ` Marc Zyngier
2017-03-28 20:50         ` Benjamin Herrenschmidt
2017-03-29  9:59           ` Brendan Higgins
2017-03-29 10:55             ` Marc Zyngier
2017-03-28  8:52   ` Benjamin Herrenschmidt
2017-03-29 10:58   ` Joel Stanley
2017-03-29 20:16     ` Brendan Higgins
2017-03-28  5:12 ` [PATCH v6 3/5] i2c: aspeed: added documentation for Aspeed I2C driver Brendan Higgins
2017-03-28  8:54   ` Benjamin Herrenschmidt
2017-03-29 10:25     ` Brendan Higgins
2017-04-03 14:22     ` Rob Herring
2017-04-03 14:24   ` Rob Herring
2017-03-28  5:12 ` [PATCH v6 4/5] i2c: aspeed: added driver for Aspeed I2C Brendan Higgins
2017-03-28  8:57   ` Benjamin Herrenschmidt
2017-03-28  9:09   ` Benjamin Herrenschmidt
2017-03-29 10:23     ` Brendan Higgins
2017-03-31  0:33   ` Joel Stanley
2017-03-31  7:33   ` Benjamin Herrenschmidt
2017-04-24 18:56     ` Brendan Higgins
2017-04-25  2:19       ` Benjamin Herrenschmidt
2017-04-25  8:32         ` Brendan Higgins
2017-04-25  8:50           ` Ryan Chen
2017-04-25  9:34             ` Benjamin Herrenschmidt
2017-04-25  9:47               ` Ryan Chen
2017-04-25 19:50                 ` Brendan Higgins
2017-04-26  0:52                   ` Ryan Chen
2017-03-28  5:12 ` [PATCH v6 5/5] i2c: aspeed: added slave support for Aspeed I2C driver Brendan Higgins
2017-03-31  0:01 ` [PATCH v6 0/5] i2c: aspeed: added driver for Aspeed I2C Andrew Jeffery

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