linux-kernel - Re: [PATCH] cfg80211/nl80211: add wifi tx power mode switching support

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Date:	Thu, 7 Jul 2016 17:30:13 +0800
From:	Wei-Ning Huang <wnhuang@...gle.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Dan Williams <dcbw@...hat.com>,
	Linux-Wireless <linux-wireless@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Sameer Nanda <snanda@...omium.org>,
	Todd Broch <tbroch@...omium.org>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH] cfg80211/nl80211: add wifi tx power mode switching support

Hi Johannes,

Thanks for the reply.

You are right that the physical antenna does not change.
When I refer to 'calibration data', it actually corresponding to how
mwifiex adjust the per-band tx power. For mwifiex, the per-band tx
power is pre-calculated based on need, and stored in DT, a vendor
command or std nl80211 message is sent
to tell the driver to switch between two set of "calibration data".
I'm aware that iwl7000 is using a vendor command to do this as well,
but instead of pre-calculate required tx power info, the tx value can
be passed along with the vendor command message.

This patch was sent originally to standardize the requirement of
sending a vendor command to the driver (so it'll be a standard nl80211
message). However, we have decided to move along with vendor command
for both mwifiex and nl80211, so this patch is not needed anymore.
Thanks for the comments!

Wei-Ning

On Tue, Jun 28, 2016 at 6:57 PM, Johannes Berg
<johannes@...solutions.net> wrote:
> On Thu, 2016-05-12 at 17:34 +0800, Wei-Ning Huang wrote:
>>
>> Johannes, I feel like being able to set calibration data at runtime
>> is something common to all wireless drivers, so instead of using
>> vendor commands what do you think if I pass the calibration data name
>> instead of using those magic constants? This way, userspace does not
>> need to know the details of what band/range power limit the driver
>> supports. It allows for flexible driver side implementation and
>> easier for userspace to control.
>>
>
> Sorry - I dropped this thread accidentally.
>
> I'm not really sure I understand the situation fully, but right now to
> me this seems very strange.
>
> The physical antennas probably don't really change between "clamshell"
> and "tablet" mode, do the physical radiation properties change enough
> to actually require different *calibration*? To me, that sounds very
> strange.
>
> Assuming they don't really change fundamentally, then I understand the
> need to set different power levels, per band/channel/whatever
> granularity. But that can be achieved in very different ways, and in
> fact if you look at Chrome then for our iwl7000 driver there we do have
> a command to do something similar (currently a vendor command, but that
> can be changed) without ever changing the *calibration*.
>
> So to me, the whole premise of the patch is confusing and/or wrong.
>
> johannes



-- 
Wei-Ning Huang, 黃偉寧 | Software Engineer, Google Inc., Taiwan |
wnhuang@...gle.com | Cell: +886 910-380678