linux-kernel - Re: [PATCH v2] regulator: s2mps11: Set default ramp delay for S2MPS11 LDOs

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Message-ID: <5715135A.4010402@osg.samsung.com>
Date:	Mon, 18 Apr 2016 13:03:22 -0400
From:	Javier Martinez Canillas <javier@....samsung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Sangbeom Kim <sbkim73@...sung.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Lee Jones <lee.jones@...aro.org>, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org
Cc:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v2] regulator: s2mps11: Set default ramp delay for S2MPS11
 LDOs

Hello Krzysztof,

On 04/18/2016 09:33 AM, Krzysztof Kozlowski wrote:
> Driver did not provide default value for ramp delay for LDOs which lead
> to warning in dmesg, e.g. on Odroid XU4:
> 
> [    1.486076] vdd_ldo9: ramp_delay not set
> [    1.506875] vddq_mmc2: ramp_delay not set
> [    1.523766] vdd_ldo15: ramp_delay not set
> [    1.544702] vdd_sd: ramp_delay not set
> 
> The datasheet for all the S2MPS1x family is inconsistent here and does
> not specify unambiguously the value of ramp delay for LDO. It mentions
> 30 mV/us in one timing diagram but then omits it completely in LDO
> regulator characteristics table (it is specified for bucks).
> 
> However the vendor kernels for Galaxy S5 and Odroid XU3 use values of 12
> mV/us or 24 mV/us.
> 
> Without the ramp delay value the consumers do not wait for voltage
> settle after changing it. Although the proper value of ramp delay for
> LDOs is unknown, it seems safer to use at least some value from
> reference kernel than to leave it unset.
> 
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
>

Reviewed-by: Javier Martinez Canillas <javier@....samsung.com>

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America