Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751780AbdHPGuW (ORCPT ); Wed, 16 Aug 2017 02:50:22 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:34827 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751687AbdHPGuT (ORCPT ); Wed, 16 Aug 2017 02:50:19 -0400 MIME-Version: 1.0 In-Reply-To: <20170815072102.23067-1-andrew@aj.id.au> References: <20170815072102.23067-1-andrew@aj.id.au> From: Joel Stanley Date: Wed, 16 Aug 2017 16:19:57 +0930 X-Google-Sender-Auth: AQ8qr6ETJz1vQ4gT11ELm8aFiuw Message-ID: Subject: Re: [PATCH] i2c: aspeed: Retain delay/setup/hold values when configuring bus frequency To: Andrew Jeffery Cc: linux-i2c@vger.kernel.org, Wolfram Sang , Brendan Higgins , Benjamin Herrenschmidt , OpenBMC Maillist , linux-aspeed@lists.ozlabs.org, Linux Kernel Mailing List , Ryan Chen Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2553 Lines: 55 On Tue, Aug 15, 2017 at 4:51 PM, Andrew Jeffery wrote: > In addition to the base, low and high clock configuration, the AC timing > register #1 on the AST2400 houses fields controlling: > > 1. tBUF: Minimum delay between Stop and Start conditions > 2. tHDSTA: Hold time for the Start condition > 3. tACST: Setup time for Start and Stop conditions, and hold time for the > Repeated Start condition > > These values are defined in hardware on the AST2500 and therefore don't > need to be set. > > aspeed_i2c_init_clk() was performing a direct write of the generated > clock values rather than a read/mask/modify/update sequence to retain > tBUF, tHDSTA and tACST, and therefore cleared the tBUF, tHDSTA and tACST > fields on the AST2400. This resulted in a delay/setup/hold time of 1 > base clock, which in some configurations is not enough for some devices > (e.g. the MAX31785 fan controller, with an APB of 48MHz and a desired > bus speed of 100kHz). > > Signed-off-by: Andrew Jeffery > --- > drivers/i2c/busses/i2c-aspeed.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c > index ee76e6dddc4b..284f8670dbeb 100644 > --- a/drivers/i2c/busses/i2c-aspeed.c > +++ b/drivers/i2c/busses/i2c-aspeed.c > @@ -53,6 +53,9 @@ > #define ASPEED_I2CD_MASTER_EN BIT(0) > > /* 0x04 : I2CD Clock and AC Timing Control Register #1 */ > +#define ASPEED_I2CD_TIME_TBUF_MASK GENMASK(31, 28) > +#define ASPEED_I2CD_TIME_THDSTA_MASK GENMASK(27, 24) > +#define ASPEED_I2CD_TIME_TACST_MASK GENMASK(23, 20) > #define ASPEED_I2CD_TIME_SCL_HIGH_SHIFT 16 > #define ASPEED_I2CD_TIME_SCL_HIGH_MASK GENMASK(19, 16) > #define ASPEED_I2CD_TIME_SCL_LOW_SHIFT 12 > @@ -744,7 +747,11 @@ static int aspeed_i2c_init_clk(struct aspeed_i2c_bus *bus) > u32 divisor, clk_reg_val; > > divisor = DIV_ROUND_UP(bus->parent_clk_frequency, bus->bus_frequency); > - clk_reg_val = bus->get_clk_reg_val(divisor); > + clk_reg_val = readl(bus->base + ASPEED_I2C_AC_TIMING_REG1); > + clk_reg_val &= (ASPEED_I2CD_TIME_TBUF_MASK | > + ASPEED_I2CD_TIME_THDSTA_MASK | > + ASPEED_I2CD_TIME_TACST_MASK); Instead of keeping the u-boot values (which appear to be hard-coded), should we instead put the known working values in the register? Cheers, Joel