linux-kernel - RFC: Regulator Framework Voltage Setting

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <CEE6BB42CAD6E947908279175AF8470A025A8A54F4@EXDCVYMBSTM006.EQ1STM.local>
Date:	Wed, 2 Jun 2010 11:18:00 +0200
From:	Linus WALLEIJ <linus.walleij@...ricsson.com>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	Bengt JONSSON <bengt.g.jonsson@...ricsson.com>,
	Sundar R IYER <sundar.iyer@...ricsson.com>
Subject: RFC: Regulator Framework Voltage Setting

Hello,

we have a question regarding the regulator_set_voltage function in the 
regulator framework (drivers/regulator/core.c). The current 
implementation checks the input min and max arguments against the 
constraints and then calls the driver set_voltage operation directly 
without checking the other consumer requests.

In our view it should respect all consumer voltage settings. Then, the 
implementation would (roughly) be to iterate through all consumers and 
make sure all of their latest requests are satisfied.

Our questions:
- Is this the correct interpretation of the current functionality?
- Is the proposed behaviour what you would expect?
- Any other problems to consider?

Below we have given an example to clarify.

Best regards,

Bengt JONSSON
Sundar R IYER
Linus WALLEIJ

Here is an example with three users (consumers) connected to the same 
regulator_dev:

rdev ------ xreg (User X)
        |--- yreg (User Y)
        |--- zreg (User Z)

The users call the regulator framework like this:

1. User X calls regulator_set_voltage(xreg, 2000000, 3000000)
2. User Y calls regulator_set_voltage(yreg, 2100000, 3100000)
3. User Z calls regulator_set_voltage(zreg, 1900000, 2900000)
4. User Y calls regulator_set_voltage(yreg, 1900000, 3100000)
5. User Z calls regulator_set_voltage(zreg, 1900000, 3100000)
6. User X calls regulator_set_voltage(xreg, 4000000, 5000000). Here the 
call should fail.

Assuming there are no constraints, with current implementation, the 
requests would be sent unchanged to the driver. What we would expect 
from the regulator framework is this:

1. The framework calls rdev->desc->ops->set_voltage(rdev, 2000000, 3000000)
2. The framework calls rdev->desc->ops->set_voltage(rdev, 2100000, 3000000)
3. The framework calls rdev->desc->ops->set_voltage(rdev, 2100000, 2900000)
4. The framework calls rdev->desc->ops->set_voltage(rdev, 2000000, 2900000)
5. The framework calls rdev->desc->ops->set_voltage(rdev, 2000000, 3000000)
6. Failed because the ranges do not overlap.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/