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From: Vitaly Andrianov <vitalya@ti.com>
To: Mark Brown <broonie@kernel.org>, Lee Jones <lee.jones@linaro.org>,
        Arnd Bergmann <arnd@arndb.de>, <linux-kernel@vger.kernel.org>
Subject: using the same regmap by multiple device drivers
Message-ID: <57740329.1080702@ti.com>
Date: Wed, 29 Jun 2016 13:19:37 -0400
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Hello,

I'm working on two drivers "crypto" and "hwrng", which use the same 
hardware module and the same block of registers. Actually the drivers 
don't need to access the same registers except several common ones.

Here is fragment of dts.

sa_subsys: subsys@1234000 {
	compatible	= "syscon";
	reg		= <0x1234000 0x1000>;
};

crypto@1234000 {
	compatible = "ti,netcp-sa-crypto";
	syscon-subsys = <&sa_subsys>;
	clocks = <&clksa>;
	.....
};

rng@1234000 {
	compatible = "ti,keystone-rng";
	syscon-subsys = <&sa_subsys>;
	clocks = <&clksa>;
};

The both drivers use

regmap = syscon_regmap_lookup_by_phandle(pdev->dev.of_node,
				  	"syscon-subsys");

to get pointers to "struct regmap".

Unfortunately I can get the first driver working only. When the second 
driver tries to call regmap_read() kernel gives "Division by zero in 
kernel" error.

Here is my question. Is that actually possible to use in regmap 
framework the same registers in multiple different drivers?

Thank you,
-Vitaly