From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 20E013939BF for ; Wed, 25 Feb 2026 16:46:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772037998; cv=none; b=LAziZo0Z/8yhPNDN3GP7s+gHCi6YuPGHZkDtlsT4PL4aojC3SZOT0GX6ITjF0LdsdeZ9y+YWlwzljBjyZrjkJBM7oDFXl/QDwkglGO+0bECxGPQrrvkaS+AFJ+HFrP7QauVbrGZSgESRNdB7xBl0RW/j/9s6Ks9FWVl+h1G7fLE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772037998; c=relaxed/simple; bh=XQkON2hH42xh3feu1yecYPdnJyLWGJ7ivFADftHZw+w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EBUw8AKSkVhPie/FsBPODXoTMEYaUAYpcGoPHdnlHwg6sQDQUneMy5VxdfqsUbFuJVjaM579EcMI2zfvpE7TBTdo0ZMM/mJMuBk6rTR1rseOnFq5bqLyWXOs+Y+BLwvC1bXWOV/MsBn/EMcC+tgjb1NiTsBZtD9W8u4UQop4qN0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=fdMV+FBN; arc=none smtp.client-ip=192.198.163.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="fdMV+FBN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1772037996; x=1803573996; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=XQkON2hH42xh3feu1yecYPdnJyLWGJ7ivFADftHZw+w=; b=fdMV+FBNEUChHEYajswxP0AMRS0YdBnDF76AXdypoS3kNIDACYt5Y4MO 9SPK31G2//cGqs/0x7KezwaCsfi0/A0Tz9KHgeBeuqq6tLL3GSOHEbF+L 12yzLktWeEUNzTmauyNjoo67fV6+onWuFl6gpBdBWOOkxtP+JNeMBU4dG HxHh3u1K/hvkcOakY8Ci6BmLibUWfFUXj4jJX5nIYZyd+REWroOoIiYMc llePMysiVhKhmAUAXd8cKqjC/ee/RuYw6ViPKVHnbnlSTGKL51fd6PJ69 OHBdeLa+93nvu1uroeSj6qL3La8wmXBwzZVX/azr1q6TY7Y5bU02cUdOV w==; X-CSE-ConnectionGUID: U9YB2yZKRZKU9uFjHBZvsw== X-CSE-MsgGUID: QARBaxa/Qj2QF/Rjdjon1w== X-IronPort-AV: E=McAfee;i="6800,10657,11712"; a="73189131" X-IronPort-AV: E=Sophos;i="6.21,310,1763452800"; d="scan'208";a="73189131" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by fmvoesa109.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Feb 2026 08:46:35 -0800 X-CSE-ConnectionGUID: +2kv7+BPQ42sVuL63eEtug== X-CSE-MsgGUID: hi7i7lsoTQq0dn4Ocmp7+Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,310,1763452800"; d="scan'208";a="215506290" Received: from gabaabhi-mobl2.amr.corp.intel.com (HELO [10.125.111.98]) ([10.125.111.98]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Feb 2026 08:46:34 -0800 Message-ID: <38d9206d-08a3-4b69-a97f-902160bd9e31@intel.com> Date: Wed, 25 Feb 2026 09:46:33 -0700 Precedence: bulk X-Mailing-List: ntb@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 06/10] NTB: epf: Document legacy doorbell slot offset in ntb_epf_peer_db_set() To: Koichiro Den , Frank.Li@nxp.com, kishon@kernel.org, jdmason@kudzu.us, mani@kernel.org, allenbh@gmail.com, kwilczynski@kernel.org, bhelgaas@google.com, jbrunet@baylibre.com, lpieralisi@kernel.org Cc: linux-pci@vger.kernel.org, ntb@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260224133459.1741537-1-den@valinux.co.jp> <20260224133459.1741537-7-den@valinux.co.jp> Content-Language: en-US From: Dave Jiang In-Reply-To: <20260224133459.1741537-7-den@valinux.co.jp> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/24/26 6:34 AM, Koichiro Den wrote: > ntb_epf_peer_db_set() uses ffs(db_bits) to select a doorbell to ring. > ffs() returns a 1-based bit index (bit 0 -> 1). > > Entry 0 is reserved for link events, so doorbell bit 0 must map to entry > 1. However, since the initial commit 812ce2f8d14e ("NTB: Add support for > EPF PCI Non-Transparent Bridge"), the implementation has been adding an > extra +1, ending up using entry 2 for bit 0. Fixing the extra increment > would break interoperability with peers running older kernels. > > Keep the legacy behavior and document the offset and the resulting slot > layout to avoid confusion when enabling per-db-vector handling. > > Signed-off-by: Koichiro Den Reviewed-by: Dave Jiang > --- > drivers/ntb/hw/epf/ntb_hw_epf.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/drivers/ntb/hw/epf/ntb_hw_epf.c b/drivers/ntb/hw/epf/ntb_hw_epf.c > index d3ecf25a5162..bce7130fec39 100644 > --- a/drivers/ntb/hw/epf/ntb_hw_epf.c > +++ b/drivers/ntb/hw/epf/ntb_hw_epf.c > @@ -43,6 +43,18 @@ > #define NTB_EPF_DB_DATA(n) (0x34 + (n) * 4) > #define NTB_EPF_DB_OFFSET(n) (0xB4 + (n) * 4) > > +/* > + * Legacy doorbell slot layout when paired with pci-epf-*ntb: > + * > + * slot 0 : reserved for link events > + * slot 1 : unused (historical extra offset) > + * slot 2 : DB#0 > + * slot 3 : DB#1 > + * ... > + * > + * Thus, NTB_EPF_MIN_DB_COUNT=3 means that we at least create vectors for > + * doorbells DB#0 and DB#1. > + */ > #define NTB_EPF_MIN_DB_COUNT 3 > #define NTB_EPF_MAX_DB_COUNT 31 > > @@ -473,6 +485,14 @@ static int ntb_epf_peer_mw_get_addr(struct ntb_dev *ntb, int idx, > static int ntb_epf_peer_db_set(struct ntb_dev *ntb, u64 db_bits) > { > struct ntb_epf_dev *ndev = ntb_ndev(ntb); > + /* > + * ffs() returns a 1-based bit index (bit 0 -> 1). > + * > + * With slot 0 reserved for link events, DB#0 would naturally map to > + * slot 1. Historically an extra +1 offset was added, so DB#0 maps to > + * slot 2 and slot 1 remains unused. Keep this mapping for > + * backward-compatibility. > + */ > u32 interrupt_num = ffs(db_bits) + 1; > struct device *dev = ndev->dev; > u32 db_entry_size;