Message-ID: <4FBDE4BD.5070701@01019freenet.de> (sfid-20120524_093953_484772_0B156F6A)
Date: Thu, 24 May 2012 09:35:25 +0200
From: Andreas Hartmann <andihartmann@01019freenet.de>
MIME-Version: 1.0
To: Helmut Schaa <helmut.schaa@googlemail.com>
CC: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
Subject: Re: [PATCH] rt2800: Initialize max_txpower to MAX_G_TXPOWER and MAX_A_TXPOWER
 respectively
References: <20120517230400.GB22418@yumi.tdiedrich.de> <CAGXE3d_Yz=-UWO+PiJkRQ7ZSBgh_fdcwsPz6FCig2VjOOoMQOg@mail.gmail.com> <20120518162158.GE22418@yumi.tdiedrich.de> <CAGXE3d8e+hYo_MT30XUW+r4-Dq6AgqLTJxD_oGnRuR94zjZ7_Q@mail.gmail.com> <4FB769DF.5060400@01019freenet.de> <4FBB5083.4000606@01019freenet.de> <CAGXE3d-2ndXX1D-JQLo6m=Osg6RRe4Z2gb_=BPrz0wASzFciNA@mail.gmail.com> <4FBB77D4.9050801@01019freenet.de> <CAGXE3d8m_0E2HGjCY9uMtj-Kahg9QCJjpsCCGjm+go6n_+V1Pg@mail.gmail.com> <4FBB8ACA.3080408@01019freenet.de>
In-Reply-To: <4FBB8ACA.3080408@01019freenet.de>
Content-Type: text/plain; charset=ISO-8859-1
Sender: linux-wireless-owner@vger.kernel.org

Andreas Hartmann wrote:
> Helmut Schaa wrote:
>> On Tue, May 22, 2012 at 1:26 PM, Andreas Hartmann
>> <andihartmann@01019freenet.de> wrote:
>>> Hello Helmut,
>>>
>>> Helmut Schaa wrote:
>>>> Hi Andreas,
>>>>
>>>> Sorry, missed your previous mail.
>>>
>>> Thanks for your response!! This made things more clear to me!
>>>
>>>> On Tue, May 22, 2012 at 10:38 AM, Andreas Hartmann
>>>> <andihartmann@01019freenet.de> wrote:
>>>>> Andreas Hartmann wrote:
>>>>>> Helmut Schaa wrote:
>>>>>>> On Fri, May 18, 2012 at 6:21 PM, Tobias Diedrich <ranma@tdiedrich.de> wrote:
>>>>>>>>> So, maybe we should do it the safe way and just register a safe default
>>>>>>>>> of 20dBm for all channels?
>>>>>>>>
>>>>>>>> AFAIU that would cap you to 20dBm even if you are in a country that
>>>>>>>> has higher limits (e.g. 27dBm in the US?).
>>>>>>>
>>>>>>> Not necessarily because the driver won't allow tx power adjustments at all
>>>>>>> if EEPROM_EIRP_MAX_TX_POWER is unused.
>>>>>>
>>>>>> This means:
>>>>>> Tx settings in cfg80211 as given by "iw reg get" e.g. are ignored
>>>>>> completely as long as EEPROM_EIRP_MAX_TX_POWER is unused.
>>>>>> Thus it is more or less chance that the device actually uses the allowed
>>>>>> / correct Tx power at all. Maybe it's too high or too low. Both would be
>>>>>> bad.
>>>
>>> [Most ralink devices have fixed max Tx power depended on the region, the
>>> device was sold]
>>>
>>>> Either we have to tune cfg80211 to allow setting the tx power by percentage
>>>> or disallow tx power control on these device or we trick cfg80211 by registering
>>>> a reasonable default value (like 20dBm) to cfg80211 but do adjustments
>>>> by percentage.
>>>>
>>>> So, if a device is actually calibrated to 17dBm but we register 20dBm
>>>> to cfg80211
>>>> and a user sets the new tx power to 17dBm we can apply the actual delta to
>>>> the device tx power configuration. Hence, the device will then
>>>> transmit with 14dBm
>>>> while cfg80211 shows 17dBm. This would be a compromise to still allow tx power
>>>> settings without having to add all the overhead to cfg80211.
>>>
>>> What about this idea: The driver gets an option to set the calibrated
>>> region (devcalreg), say US. This is a static value in respect of the device.
>>> If the user operates the device in DE, he just would have to change the
>>> value of cfg80211 from US to DE.
>>>
>>> Device sold in US
>>> =================
>>>
>>> Device operated in US
>>> devcalreg=US                                    23dBm
>>> cfg80211=US             100% max Tx power       23dBm
>>>
>>> Device operated in DE
>>> devcalreg=US                                    23dBm
>>> cfg80211=DE             87%  max Tx power       20dBm

Well, I just saw, that the legacy driver
2010_0915_RT3572_Linux_STA_v2.4.0.2 defines in include/rtmp.h

UCHAR TxPower; // in unit of mW

Therefore my calculation above would have been wrong, if I got it right.

23dBm equate 199mW
20dBm equate 100mW

To get the ralink device work with the reduced legal Tx power (20dBm
instead of 23dBm), I would have to use 50% and not 87%.

>>>
>>> If cfg80211 is set to a region which allows higher values, the
>>> percentage would be >100%, but this could be probably easily prohibited.
>>>
>>> If the user doesn't provide devcalreg your default value gets applied.
>>>
>>> The difference to your idea is, that the "default" could be dynamically
>>> derived from cfg80211 on the basis of the devcalreg. This would prohibit
>>> the problem you showed above.
>>
>> Understood, but that would require the user to know the domain the
>> device is calibrated for.
> 
> Why should he not know this? If it is really not known, your default is
> applied hence nothing is lost.
> 
>> I think we should just always run the device at 100% but add an option in
>> the future to allow rx power reduction by percentage.
> 
> Hmmm, but this requires the user to know even more:
> - For which domain is the device originally calibrated?
> - What's the allowed max value of this domain?
> - What's the allowed max value of the new domain the device should
> operate now?
> - Calculate the percentage < 100% to get the correct Tx-power.

- The user has to know, that the base of the percentage is mW and he has
to take care of the different units and he has to know how to handle them.


I do not think, that it is a good idea to leave the user alone with
finding the correct new percentage.

Please, think again about this point - or did I get something wrong?

I know it is much more time and effort to implement it, but it would be
much more user friendly :-).


Thanks,
kind regards,
Andreas