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Message-ID: <YMxueLOhlXjy1ZRH@smile.fi.intel.com>
Date: Fri, 18 Jun 2021 12:59:20 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Jamin Lin <jamin_lin@...eedtech.com>
Cc: Rob Herring <robh+dt@...nel.org>, Joel Stanley <joel@....id.au>,
Andrew Jeffery <andrew@...id.au>,
Philipp Zabel <p.zabel@...gutronix.de>,
Wolfram Sang <wsa+renesas@...g-engineering.com>,
Arnd Bergmann <arnd@...db.de>, Jean Delvare <jdelvare@...e.de>,
Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
Khalil Blaiech <kblaiech@...lanox.com>,
Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Bence Csókás <bence98@....bme.hu>,
Yicong Yang <yangyicong@...ilicon.com>,
Mike Rapoport <rppt@...nel.org>,
Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
Ryan Chen <ryan_chen@...eedtech.com>,
"open list:I2C SUBSYSTEM HOST DRIVERS" <linux-i2c@...r.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@...r.kernel.org>,
"moderated list:ARM/ASPEED MACHINE SUPPORT"
<linux-arm-kernel@...ts.infradead.org>,
"moderated list:ARM/ASPEED MACHINE SUPPORT"
<linux-aspeed@...ts.ozlabs.org>,
open list <linux-kernel@...r.kernel.org>,
ChiaWei Wang <chiawei_wang@...eedtech.com>,
Troy Lee <troy_lee@...eedtech.com>,
Steven Lee <steven_lee@...eedtech.com>
Subject: Re: [PATCH 3/3] i2c:support new register set for ast2600
On Fri, Jun 18, 2021 at 11:53:41AM +0800, Jamin Lin wrote:
> The 06/17/2021 10:33, Andy Shevchenko wrote:
> > On Thu, Jun 17, 2021 at 05:43:40PM +0800, Jamin Lin wrote:
...
> > > + *
> > > + * This program is free software; you can redistribute it and/or modify
> > > + * it under the terms of the GNU General Public License version 2 as
> > > + * published by the Free Software Foundation.
> >
> > SPDX covers this.
> >
> Will change as following what do you think?
> // SPDX-License-Identifier: GPL-2.0-or-later
> /*
> * Aspeed I2C Interrupt Controller.
> * Copyright (C) ASPEED Technology Inc.
> * Ryan Chen <ryan_chen@...eedtech.com>
> */
Yes, something like this.
...
> > > +static const struct aspeed_i2c_base_clk i2c_base_clk[BASE_CLK_COUNT] = {
> > > + /* name target_freq */
> > > + { "base_clk0", 1000000 }, /* 1M */
> > > + { "base_clk1", 4000000 }, /* 4M */
> > > + { "base_clk2", 10000000 }, /* 10M */
> > > + { "base_clk3", 40000000 }, /* 40M */
> > > +};
> >
> > Why it's not provided as the clock provider(s)?
> According to the design of ASPEED AST2600 SOC, the I2C bus is connected to PHB bus.
> The clock driver provides PHB clock and its default frequency is 100MHZ.
> AST2600 support the bus frequency of I2C from 0.1kbps to 5Mbps if PHB clock is 50MHZ.
> To meet the different bus frequency of I2C, we use this programmer to calculate the divider to
> change the base clock.
> For example,
> It calculates divider to change base_clock 1 to 1M to support I2C bus frequency 100KHZ
> It calculates divider to change base_clock 2 to 4M to support I2C bus frequency 400KHZ
My question is, why don't you provide a clock provider (under drivers/clk) for
this platform and use it instead?
...
> > > + struct clk_hw_onecell_data *onecell;
> > > + struct clk_hw *hw;
> > > + int err;
> > > + u32 clk_divider = 0;
> > > + int i, j;
> > > + unsigned long base_freq;
> >
> > Use reversed xmas tree order for all these blocks.
> >
> > The rule of thumb, btw, that any comment applies to all similar places by
> > default (independently on which line it was given against).
> >
> Do you mena change as following?
> struct clk_hw_onecell_data *onecell;
> unsigned long base_freq;
> u32 clk_divider = 0;
> struct clk_hw *hw;
> int err;
> int i;
> int j;
Yes.
...
> > > + for (i = 0; i < 0xff; i++) {
> > > + /*
> > > + * i maps to div:
> > > + * 0x00: div 1
> > > + * 0x01: div 1.5
> > > + * 0x02: div 2
> > > + * 0x03: div 2.5
> > > + * 0x04: div 3
> > > + * ...
> > > + * 0xFE: div 128
> > > + * 0xFF: div 128.5
> > > + */
> > > + base_freq = base_clk * 2 / (2 + i);
> > > + if (base_freq <= i2c_base_clk[j].base_freq)
> > > + break;
> > > + }
> >
> > oAre yuo sure you can't eliminate the entire for-loop? Think about it a bit,
> > please.
> >
> What do you think if we use "lookup table" instaed of above for loop?
Besides that it should be a part of clock provider, no, you may use a formula
(bit operations and so on).
...
> > > + i2c_ic->rst = devm_reset_control_get_exclusive(&pdev->dev, NULL);
> > > + if (IS_ERR(i2c_ic->rst)) {
> >
> > > + dev_dbg(&pdev->dev,
> > > + "missing or invalid reset controller device tree entry");
> >
> > Make it optional.
> Can I change to use "dev_err"?
What I meant here is to make the reset optional (there is even specific API for
that) and return an error in that case.
> > > + } else {
> > > + /* SCU I2C Reset */
> > > + reset_control_assert(i2c_ic->rst);
> > > + udelay(3);
> > > + reset_control_deassert(i2c_ic->rst);
> > > + }
...
> > > +static struct ast_i2c_timing_table aspeed_old_i2c_timing_table[] = {
> >
> > What the ... is this for?!
> AST2600 support old/new register set for I2C controller.
> This lookup table is used to find the divisor for the specific I2C bus
> frequency for AST2600 I2C controller with old register set.
> For example
> If I2C bus frequency is 100KHZ and PHB clock is 100MHZ, it will find this table
> because 100000000/1024 < 100000
> "{ 1024, 0x00000300 | (0x5) | (0xf << 20) | (0xf << 16) | (0xf << 12) }"
Can't you derive it by formula(s)?
> > > + /* Divisor : Base Clock : tCKHighMin : tCK High : tCK Low */
> > > + /* Divisor : [3:0] : [23: 20] : [19:16]: [15:12] */
> > > +};
--
With Best Regards,
Andy Shevchenko
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