From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 1A202272E6D; Tue, 23 Jun 2026 15:48:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782229695; cv=none; b=Ku5vNpvmHLKdsPcIfr7c2dB4Eb9zc59LexKMoqwiE5bPm5/cdZflUyLSoE1Sl33U2DAa98Wb72fN8UZ96vRd06uTee0YX1CISWMB44O4phc6+9p+7SIklvN23rPPukRghvfeKCMfYy+gNq5mQM73xprzQjtMUOdW6E7JWRiTdOw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782229695; c=relaxed/simple; bh=NJqkEZcWa1A5YciYaSbIuAPL/MnbLkuiSpwUoNgaw8A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qHpF0Wau0DWJRIPkmEVXKvxwlQUkkLKh7xMcV8GNb5Y+801wJN/TrsCVW+n+HfJYssiKaElOR4fLCvy9AS0TM+hg4u69deVOfuBOnMn8RvHHyrmM2dyBn6k3J8vat/RI9S9pRb9oeiYC3ff5oXlYvbp+tTwJGOf6OaXNLKqOBHs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=Bo+JWdlj; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="Bo+JWdlj" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D130016F8; Tue, 23 Jun 2026 08:48:08 -0700 (PDT) Received: from [10.2.212.23] (e121345-lin.cambridge.arm.com [10.2.212.23]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CDC803F62B; Tue, 23 Jun 2026 08:48:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1782229693; bh=NJqkEZcWa1A5YciYaSbIuAPL/MnbLkuiSpwUoNgaw8A=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Bo+JWdlj2ADWTVgzFv+6PqCl48iOPpg92u2k+0c2TeJ3N/RurCTpn86f1qiS/jSsR 63I52Za56NNbj3HMlm9X7FzRlLcP42vWhhLC7JrK3xQqxot8x772iEorlLECXDJgNp W2rPKXAW7W9lWYjrw/Dk3RKu7VEAkBmxVWDXoxGg= Message-ID: <81a9d212-996e-42e1-aabf-b120a13e94c3@arm.com> Date: Tue, 23 Jun 2026 16:48:06 +0100 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: [PATCH v3 1/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE To: Matt Evans , "Tian, Kevin" , Pranjal Shrivastava Cc: Alex Williamson , Leon Romanovsky , Jason Gunthorpe , Alex Mastro , =?UTF-8?Q?Christian_K=C3=B6nig?= , Bjorn Helgaas , Logan Gunthorpe , Mahmoud Adam , David Matlack , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Sumit Semwal , Ankit Agrawal , Alistair Popple , "Kasireddy, Vivek" , "linux-kernel@vger.kernel.org" , "linux-media@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "linaro-mm-sig@lists.linaro.org" , "kvm@vger.kernel.org" , "linux-pci@vger.kernel.org" References: <20260610154327.37758-1-matt@ozlabs.org> <20260610154327.37758-2-matt@ozlabs.org> <0dfadf98-a904-4e6a-b078-5caf27bc7922@ozlabs.org> From: Robin Murphy Content-Language: en-GB In-Reply-To: <0dfadf98-a904-4e6a-b078-5caf27bc7922@ozlabs.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/06/2026 3:31 pm, Matt Evans wrote: > Hi Kevin, Pranjal, (+Robin, hi!) Oh hey there! :) > On 12/06/2026 04:39, Tian, Kevin wrote: >>> From: Pranjal Shrivastava >>> Sent: Friday, June 12, 2026 2:38 AM >>> >>> On Wed, Jun 10, 2026 at 04:43:15PM +0100, Matt Evans wrote: >>>> --- a/drivers/pci/Kconfig >>>> +++ b/drivers/pci/Kconfig >>>> @@ -206,11 +206,7 @@ config PCIE_TPH >>>> config PCI_P2PDMA >>>> bool "PCI peer-to-peer transfer support" >>>> depends on ZONE_DEVICE >>>> - # >>>> - # The need for the scatterlist DMA bus address flag means PCI >>> P2PDMA >>>> - # requires 64bit >>>> - # >>>> - depends on 64BIT >>>> + select PCI_P2PDMA_CORE >>>> select GENERIC_ALLOCATOR >>>> select NEED_SG_DMA_FLAGS >>>> help >>> >>> Nit: Did we drop depends on 64BIT intentionally here? I guess the full >>> PCI_P2PDMA stack still selects NEED_SG_DMA_FLAGS? IIRC, >>> NEED_SG_DMA_FLAGS doesn't select 64BIT? >> >> seems that comment is stale. According to the commit msg: >> >> " it would make vfio-pci only available if CONFIG_ZONE_DEVICE is >> present (e.g. 64-bit systems), " >> >> so it sounds a redundant dependency hence is removed. > > This was intentional. In practice there is still a dependency on 64BIT > for PCI_P2PDMA, but it is because of ZONE_DEVICE (and mem hotplug). The > key need is PCI_P2PDMA_CORE is available on !64BIT for VFIO, but I > didn't see a requirement from PCI_P2PDMA itself (as opposed to its > dependencies). If I've missed one, I can put it back... > > But NEED_SG_DMA_FLAGS doesn't smell quite right; I see from comments in > > af2880ec44021 ("scatterlist: add dedicated config for DMA flags") > > that it assumes 64BIT, but it seems to be missing a "depends on 64BIT". > > Robin -- should that depend on 64BIT? Indeed, looking at the history it seems like that was overlooked, but it worked out at the time since the only selector of NEED_SG_DMA_FLAGS was PCI_P2PDMA as you say. If we're now generalising then moving the explicit 64BIT dependency to NEED_SG_DMA_FLAGS itself sounds like the right thing to do. Cheers, Robin.