From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Lunn Subject: Re: [PATCH] net: fec: Ensure clocks are enabled while using mdio bus Date: Sun, 14 Jun 2015 16:41:18 +0200 Message-ID: <20150614144118.GA7800@lunn.ch> References: <1434123545-13549-1-git-send-email-andrew@lunn.ch> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , Cory Tusar , netdev To: Duan Andy Return-path: Received: from vps0.lunn.ch ([178.209.37.122]:55793 "EHLO vps0.lunn.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751524AbbFNOrF (ORCPT ); Sun, 14 Jun 2015 10:47:05 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Sun, Jun 14, 2015 at 08:07:12AM +0000, Duan Andy wrote: > From: Andrew Lunn Sent: Friday, June 12, 2015 11:39 PM > > To: David Miller > > Cc: Duan Fugang-B38611; Cory Tusar; netdev; Andrew Lunn > > Subject: [PATCH] net: fec: Ensure clocks are enabled while using mdio bus > > > > When a switch is attached to the mdio bus, the mdio bus can be used while > > the interface is not open. If the clocks are not enabled, MDIO > > reads/writes will simply time out. So enable the clocks before starting a > > transaction, and disable them afterwards. The CCF performs reference > > counting so the clocks will only be disabled if there are no other users. > > > > Signed-off-by: Andrew Lunn > > --- > > NAK the patch. > i.MX series MDIO bus is a part of ENET controller. If the eth > interface is not open, all clocks including MDIO bus clock are not > enabled for power saving. Where do you see a power saving regression in this code? It is not as if i just unconditionally turn the clocks on. As the comment says, at the start of an MDIO transaction, the clocks are enabled. At the end of a transaction, they are disabled again. If you don't have a switch connected, there will be no transactions, hence no change to power savings. > In general, if you want to use mdio bus net interface must be > running status. This is not true for a number of Ethernet devices. All those currently used with DSA allow MDIO transactions at any time. Andrew