From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:32924 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751297AbdL2QYm (ORCPT ); Fri, 29 Dec 2017 11:24:42 -0500 Date: Fri, 29 Dec 2017 16:24:36 +0000 From: Jonathan Cameron To: Eugen Hristev Cc: , , , , , , , , Subject: Re: [PATCH 11/14] iio: adc: at91-sama5d2_adc: optimize scan index for diff channels Message-ID: <20171229162436.5fe18421@archlinux> In-Reply-To: <1513955241-10985-12-git-send-email-eugen.hristev@microchip.com> References: <1513955241-10985-1-git-send-email-eugen.hristev@microchip.com> <1513955241-10985-12-git-send-email-eugen.hristev@microchip.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-iio-owner@vger.kernel.org List-Id: linux-iio@vger.kernel.org On Fri, 22 Dec 2017 17:07:18 +0200 Eugen Hristev wrote: > Optimize the scan index for the differential channels. Before, it > was single channel count + index of the first single channel > number of the differential pair. (e.g. 11+0, +2, +4, etc.) > Divide that number by two (since it's always even), and add it up > as a scan index to have consecutive numbered channels in the > index. Why? This is odd as it stands, but that isn't a strong enough reason to fix it. This is making a userspace ABI change. We need a very strong argument for why it is necessary and also why existing userspace won't care. > > Signed-off-by: Eugen Hristev > --- > drivers/iio/adc/at91-sama5d2_adc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c > index 7b9febc..9610393 100644 > --- a/drivers/iio/adc/at91-sama5d2_adc.c > +++ b/drivers/iio/adc/at91-sama5d2_adc.c > @@ -209,7 +209,7 @@ > .channel = num, \ > .channel2 = num2, \ > .address = addr, \ > - .scan_index = num + AT91_SAMA5D2_SINGLE_CHAN_CNT, \ > + .scan_index = (num >> 1) + AT91_SAMA5D2_SINGLE_CHAN_CNT,\ > .scan_type = { \ > .sign = 's', \ > .realbits = 12, \