From patchwork Mon Sep 11 13:14:11 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bryan O'Donoghue X-Patchwork-Id: 721528 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 38057CA0EC4 for ; Mon, 11 Sep 2023 21:19:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344153AbjIKVN0 (ORCPT ); Mon, 11 Sep 2023 17:13:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40602 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237834AbjIKNOi (ORCPT ); Mon, 11 Sep 2023 09:14:38 -0400 Received: from mail-ej1-x634.google.com (mail-ej1-x634.google.com [IPv6:2a00:1450:4864:20::634]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B084EE for ; Mon, 11 Sep 2023 06:14:34 -0700 (PDT) Received: by mail-ej1-x634.google.com with SMTP id a640c23a62f3a-9aa2468bdb4so161586866b.0 for ; Mon, 11 Sep 2023 06:14:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1694438073; x=1695042873; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=jRNeftuB+INOMHeCbSOiUEWxB5DnzuRjYAHI6QDDXkA=; b=Vigeez2weEsges0RIcdXWa/U3nqvHSmFBU3YWORDkgLIXIrVtgQEDbDBi5p8hdEGZ/ aG9mtTIJjVQnbUtD6frCGm9NzTxya9/DvEI+PPu1WhySMzhZ0BaAJpwRgcbmogXuA5tg S8Wpe2KCRPTBgDkXaw+J+J3FvvUM1Hdu3pVXosrlYWFUy8PSZiNXQFTJVEpayQFxjSyr kinkI/nGFoQM+Qfw5360zji+JpPziGYF3OcfzwbTJ3obIXJbBWk+41i+We4yyaun+LOu w4V4crhu5UP8a/9+DH+PWu1cKc0cZ/NMOGNaROCkRkPmAbaYRmbQSzwo/IUrWZY6I+QF uK6Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1694438073; x=1695042873; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=jRNeftuB+INOMHeCbSOiUEWxB5DnzuRjYAHI6QDDXkA=; b=h0FuJ+nomCpVLrz/q0ZaxujJxdMf9FAbQIM8HjH17/DDjHH57lxUOLvZVDs/tDpqcF YQoETH6vIp4idWiU7lcUvTqFw5Hr2/KDYq0VzCLMW/Vpk7HC9GmYS3E2DvoA4pRoO25a QfO2Ff1jE7WEl3WWAHfglmIvSphOg5LcJ5bmacuqNS6ZBzJgqYWJ5Xb4It/kJdwzHimY iJhziVXfsZ4SqqdvXVZpRAg0jC0cue98ElSFaHmJmDztM3ck98TNHQ5pB8dHgUhmEBVa XkH6uucSLb5rFMNTRHKiqiM23fGFPKYbtZEXANQtYq+YYeffhgJQnJudGdkYPZnPtlb0 MFmg== X-Gm-Message-State: AOJu0YwHxbe18W74ifnVwg8Z3pXZOjFOI68AllC0QZC2+MRFTRxnX0Tw GpDmctfbnVemTqXu2COcFZ2+Iw== X-Google-Smtp-Source: AGHT+IHlCK86n0VeHZ+HtSrI9mh5xjoWNZuc9ZOAbu0C2O0EAitiz9ZVW48URQEVox9KobL72BbK+w== X-Received: by 2002:a17:906:5347:b0:9a9:e41c:bcb5 with SMTP id j7-20020a170906534700b009a9e41cbcb5mr9086672ejo.76.1694438072876; Mon, 11 Sep 2023 06:14:32 -0700 (PDT) Received: from sagittarius-a.chello.ie (188-141-3-169.dynamic.upc.ie. [188.141.3.169]) by smtp.gmail.com with ESMTPSA id kt8-20020a170906aac800b00988e953a586sm5313648ejb.61.2023.09.11.06.14.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 11 Sep 2023 06:14:32 -0700 (PDT) From: Bryan O'Donoghue To: rfoss@kernel.org, todor.too@gmail.com, bryan.odonoghue@linaro.org, agross@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org, mchehab@kernel.org, hverkuil-cisco@xs4all.nl, laurent.pinchart@ideasonboard.com, sakari.ailus@linux.intel.com, andrey.konovalov@linaro.org Cc: linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v5 17/17] media: qcom: camss: Comment CSID dt_id field Date: Mon, 11 Sep 2023 14:14:11 +0100 Message-ID: <20230911131411.196033-18-bryan.odonoghue@linaro.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20230911131411.196033-1-bryan.odonoghue@linaro.org> References: <20230911131411.196033-1-bryan.odonoghue@linaro.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org 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 | 5 +++++ 1 file changed, 5 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..cee50fc87e9de 100644 --- a/drivers/media/platform/qcom/camss/camss-csid-gen2.c +++ b/drivers/media/platform/qcom/camss/camss-csid-gen2.c @@ -352,6 +352,11 @@ static void __csid_configure_stream(struct csid_device *csid, u8 enable, u8 vc) phy_sel = csid->phy.csiphy_id; if (enable) { + /* + * A value caled 'CID' gets generated internal to CAMSS logic + * which is a concatenation of [vc:6 | dt_id:2] hence we reuse + * the least significant two bits of the VC to 'stuff' the CID value. + */ u8 dt_id = vc; if (tg->enabled) {