From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7AD92E810D5 for ; Wed, 27 Sep 2023 11:42:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231524AbjI0Lmf (ORCPT ); Wed, 27 Sep 2023 07:42:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50714 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231132AbjI0Lma (ORCPT ); Wed, 27 Sep 2023 07:42:30 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 07929F3; Wed, 27 Sep 2023 04:42:29 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68382C433CA; Wed, 27 Sep 2023 11:42:26 +0000 (UTC) Message-ID: Date: Wed, 27 Sep 2023 13:42:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RESEND PATCH v6 17/17] media: qcom: camss: Comment CSID dt_id field Content-Language: en-US, nl To: Bryan O'Donoghue , linux-arm-msm@vger.kernel.org, linux-media@vger.kernel.org, laurent.pinchart@ideasonboard.com, rfoss@kernel.org, todor.too@gmail.com, agross@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org, mchehab@kernel.org, sakari.ailus@linux.intel.com, andrey.konovalov@linaro.org Cc: linux-kernel@vger.kernel.org References: <20230925154707.837542-1-bryan.odonoghue@linaro.org> <20230925154707.837542-18-bryan.odonoghue@linaro.org> From: Hans Verkuil Autocrypt: addr=hverkuil@xs4all.nl; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/09/2023 17:47, Bryan O'Donoghue wrote: > Digging into the documentation we find that the DT_ID bitfield is used to > map the six bit DT to a two bit ID code. This value is concatenated to the > VC bitfield to create a CID value. DT_ID is the two least significant bits > of CID and VC the most significant bits. > > Originally we set dt_id = vc * 4 in and then subsequently set dt_id = vc. > > commit 3c4ed72a16bc ("media: camss: sm8250: Virtual channels for CSID") > silently fixed the multiplication by four which would give a better > value for the generated CID without mentioning what was being done or why. > > Next up I haplessly changed the value back to "dt_id = vc * 4" since there > didn't appear to be any logic behind it. > > Hans asked what the change was for and I honestly couldn't remember the > provenance of it, so I dug in. > > Link: https://lore.kernel.org/linux-arm-msm/edd4bf9b-0e1b-883c-1a4d-50f4102c3924@xs4all.nl/ > > Add a comment so the next hapless programmer doesn't make this same > mistake. > > Signed-off-by: Bryan O'Donoghue > --- > drivers/media/platform/qcom/camss/camss-csid-gen2.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/media/platform/qcom/camss/camss-csid-gen2.c b/drivers/media/platform/qcom/camss/camss-csid-gen2.c > index 6ba2b10326444..791f27b18c394 100644 > --- a/drivers/media/platform/qcom/camss/camss-csid-gen2.c > +++ b/drivers/media/platform/qcom/camss/camss-csid-gen2.c > @@ -352,6 +352,18 @@ static void __csid_configure_stream(struct csid_device *csid, u8 enable, u8 vc) > phy_sel = csid->phy.csiphy_id; > > if (enable) { > + /* > + * DT_ID is a two bit bitfield that is concatenated with > + * the four least significant bits of the six bit VC > + * bitfield to generate an internal CID value. > + * > + * CSID_RDI_CFG0(vc) > + * DT_ID : 28:27 > + * VC : 26:22 This is 5 bits, not 6 bits as the comment above says. Which is right? > + * DT : 21:16 > + * > + * CID : VC 3:0 << 2 | DT_ID 1:0 > + */ > u8 dt_id = vc; So if dt_id is 2 bits, and vc can be more than 2 bits in the future, shouldn't this read "vc & 3"? Regards, Hans > > if (tg->enabled) {