linux-kernel - Re: [PATCH] ARM: dts: am437x-sk-evm: Reduce i2c0 bus speed for tps65218

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Message-ID: <20160617095925.GD22406@atomide.com>
Date:	Fri, 17 Jun 2016 02:59:26 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Keerthy <j-keerthy@...com>
Cc:	robh+dt@...nel.org, mark.rutland@....com, d-gerlach@...com,
	nm@...com, linux-omap@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Franklin S Cooper Jr <fcooper@...com>,
	Aparna Balasubramanian <aparnab@...com>
Subject: Re: [PATCH] ARM: dts: am437x-sk-evm: Reduce i2c0 bus speed for
 tps65218

* Keerthy <j-keerthy@...com> [160614 23:18]:
> From: Dave Gerlach <d-gerlach@...com>
> 
> Based on the latest timing specifications for the TPS65218 from the data
> sheet, http://www.ti.com/lit/ds/symlink/tps65218.pdf, document SLDS206
> from November 2014, we must change the i2c bus speed to better fit within
> the minimum high SCL time required for proper i2c transfer.
> 
> When running at 400khz, measurements show that SCL spends
> 0.8125 uS/1.666 uS high/low which violates the requirement for minimum
> high period of SCL provided in datasheet Table 7.6 which is 1 uS.
> Switching to 100khz gives us 5 uS/5 uS high/low which both fall above
> the minimum given values for 100 khz, 4.0 uS/4.7 uS high/low.
> 
> Without this patch occasionally a voltage set operation from the kernel
> will appear to have worked but the actual voltage reflected on the PMIC
> will not have updated, causing problems especially with cpufreq that may
> update to a higher OPP without actually raising the voltage on DCDC2,
> leading to a hang.

Applying into omap-for-v4.7/fixes thanks.

Tony