From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.18]) (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 751E024DCE5 for ; Tue, 2 Dec 2025 02:22:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764642125; cv=none; b=Cfw6/c4i+m6jnmugV9cU/Cbzv2jxNmVv6HG6DTL3rCTxVL8DXtRnOQ5Win5HZxygL9BEMDBOcb7UY7iysb7dumxRz6Woz3F2xPek3LZ594CZIqZBN5zFNUrA1Jn+sQUEn2GJT3J8O1ZmEuBIluXWPpbXW9M11pg6ubxB9stdRmA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764642125; c=relaxed/simple; bh=dpas8Oj4TRsn+P0O6MoXpBjhKhSe8cngwuBQy05Th6Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ndphZ1qDRrUDCpfMW3ake0L7Ry9L4JqIeihY7AZETKX/tZzVB+7fwgbcpaXRdqVzGubUzYgK7qkZj+ZB0rOXSDwrLS2unf3TDjDI1aQMzV/DkByQUTKRPouTgC0CcMPn1pzhVzstbrAbU5uByzNiaYzdYkiyUjEo4Pz+KIFVSP4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=pass smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=G7+7BVla; arc=none smtp.client-ip=192.198.163.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="G7+7BVla" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1764642122; x=1796178122; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=dpas8Oj4TRsn+P0O6MoXpBjhKhSe8cngwuBQy05Th6Q=; b=G7+7BVlaSa0TkZeJrwLON4BUi79vdd/kaKTKKSBSjHrddEr+83Fn4d9e cZymeYnyJzwqCPioixWII+7U92tXOkpH6eb/u3L6k39uEkfUFwbZK5nxN EQbNaUwesO/9vNWv5lKilljvgwuVtakZvTz/343uE2JJnnc/Gd1TLJ2wy IZUFInNyGrJ+WAFOt0lqxMo61JjW5ax867gL91ffENJcbaDEhjWTZFnpF L12OtGPRvw2h2DoHsYH84CQtmiI8Sj1XtKfv9KAANeOlTKNitC/EN4JAN lwC9wFhw0YsTmCIvrWKrUFOZO24cFkMkvMhnAJyoG2FqliIbUcMK7e1x5 A==; X-CSE-ConnectionGUID: VlhMRch3SoKU2KL3ZIaJIQ== X-CSE-MsgGUID: OZBkMcvgTmG5ZVhYOu0jAg== X-IronPort-AV: E=McAfee;i="6800,10657,11630"; a="65785610" X-IronPort-AV: E=Sophos;i="6.20,241,1758610800"; d="scan'208";a="65785610" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by fmvoesa112.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Dec 2025 18:22:02 -0800 X-CSE-ConnectionGUID: oA3R/031T5aNIEmwYitPOw== X-CSE-MsgGUID: DYgA30aVTUKAxheDoipu+Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.20,241,1758610800"; d="scan'208";a="194118262" Received: from allen-sbox.sh.intel.com (HELO [10.239.159.30]) ([10.239.159.30]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Dec 2025 18:21:58 -0800 Message-ID: Date: Tue, 2 Dec 2025 10:17:34 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 2/8] iommu: Add a helper to check if any iommu device is registered To: Jacob Pan , linux-kernel@vger.kernel.org, "iommu@lists.linux.dev" , Jason Gunthorpe , Alex Williamson , Joerg Roedel , Will Deacon , Robin Murphy , Nicolin Chen , "Tian, Kevin" , "Liu, Yi L" Cc: skhawaja@google.com, pasha.tatashin@soleen.com, Zhang Yu , Jean Philippe-Brucker , David Matlack References: <20251201173012.18371-1-jacob.pan@linux.microsoft.com> <20251201173012.18371-3-jacob.pan@linux.microsoft.com> Content-Language: en-US From: Baolu Lu In-Reply-To: <20251201173012.18371-3-jacob.pan@linux.microsoft.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Jacob, On 12/2/25 01:30, Jacob Pan wrote: > The dummy IOMMU driver for No-IOMMU mode should only be active when > no real IOMMU devices are present in the system. Introduce a helper > to check this condition, ensuring that the dummy driver does not > interfere when hardware-backed IOMMU support is available. > > Signed-off-by: Jacob Pan > --- > drivers/iommu/iommu.c | 10 ++++++++++ > include/linux/iommu.h | 1 + > 2 files changed, 11 insertions(+) > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 0df914a04064..958f612bf176 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -2895,6 +2895,16 @@ static const struct iommu_device *iommu_from_fwnode(const struct fwnode_handle * > return ret; > } > > +bool iommu_is_registered(void) > +{ > + bool registered; > + > + spin_lock(&iommu_device_lock); > + registered = !list_empty(&iommu_device_list); > + spin_unlock(&iommu_device_lock); > + return registered; > +} IOMMU devices might be added by calling iommu_device_register() at any time. Therefore, an empty iommu_device_list does not necessarily mean that "no real IOMMU devices are present in the system." Thanks, baolu