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From: Alexander Kurz <akurz@blala.de>
To: Alexander Shiyan <shc_work@mail.ru>,
	Sascha Hauer <s.hauer@pengutronix.de>
Cc: barebox@lists.infradead.org
Subject: mc13xxx: Define maximum SPI clock frequency global to driver
Date: Tue, 19 Jul 2016 19:18:35 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.00.1607191912280.9957@blala.de> (raw)

Hi,
I just ran into a problem resulting from patch 6e18b3a48ee4
("mc13xxx: Define maximum SPI clock frequency global to driver").

On a kindle2 board the SPI communication between an iMX31 and a MC13783 
won't work at 20MHz. Unfortunately both ICs are BGA mounted blocking any 
access with scope probes. Attempts to tweak the pad properties to
PAD_CTL_DRV_HIGH | PAD_CTL_SRE_FAST | PAD_CTL_100K_PU
did not solve the problem - anyway this is a battery powered device where
the original implementers took great care on long battery life,
e.g. PAD_CTL_DRV_HIGH should not be nessesary for PMIC control.

I do not see any way to override the 20MHz bitrate from board code, and 
since the PMIC access is not time critical on an ebook-reader my choice
would be rather 200kHz.

Is there any way to override the driver supplied default max_speed_hz?
If not, my proposal is to either
* revert this patch and let the board code choose frequency
or
* reduce the speed to some common acceptable rate, e.g. 6MHz are fine

How was this solved with other SPI devices?

Cheers, Alexander


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             reply	other threads:[~2016-07-19 17:21 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-19 17:18 Alexander Kurz [this message]
2016-07-19 18:15 ` Alexander Shiyan
2016-07-19 20:31   ` Alexander Kurz

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