From: Robin Murphy <robin.murphy@arm.com>
To: Niklas Schnelle <schnelle@linux.ibm.com>,
Joerg Roedel <joro@8bytes.org>,
Matthew Rosato <mjrosato@linux.ibm.com>,
Will Deacon <will@kernel.org>,
Wenjia Zhang <wenjia@linux.ibm.com>,
Jason Gunthorpe <jgg@ziepe.ca>
Cc: Gerd Bayer <gbayer@linux.ibm.com>,
Julian Ruess <julianr@linux.ibm.com>,
Pierre Morel <pmorel@linux.ibm.com>,
Alexandra Winter <wintera@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Hector Martin <marcan@marcan.st>, Sven Peter <sven@svenpeter.dev>,
Alyssa Rosenzweig <alyssa@rosenzweig.io>,
David Woodhouse <dwmw2@infradead.org>,
Lu Baolu <baolu.lu@linux.intel.com>,
Andy Gross <agross@kernel.org>,
Bjorn Andersson <andersson@kernel.org>,
Konrad Dybcio <konrad.dybcio@linaro.org>,
Yong Wu <yong.wu@mediatek.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@collabora.com>,
Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
Orson Zhai <orsonzhai@gmail.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Chunyan Zhang <zhang.lyra@gmail.com>,
Chen-Yu Tsai <wens@csie.org>,
Jernej Skrabec <jernej.skrabec@gmail.com>,
Samuel Holland <samuel@sholland.org>,
Thierry Reding <thierry.reding@gmail.com>,
Krishna Reddy <vdumpa@nvidia.com>,
Jonathan Hunter <jonathanh@nvidia.com>,
Jonathan Corbet <corbet@lwn.net>,
linux-s390@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
asahi@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
linux-arm-msm@vger.kernel.org,
linux-mediatek@lists.infradead.org, linux-sunxi@lists.linux.dev,
linux-tegra@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH v11 5/6] iommu/dma: Allow a single FQ in addition to per-CPU FQs
Date: Tue, 29 Aug 2023 16:39:42 +0100 [thread overview]
Message-ID: <f2a46201-d807-d7af-bf84-8c99b33cd916@arm.com> (raw)
In-Reply-To: <b46210ce00b46ce42b8487e5670cc56b4458031f.camel@linux.ibm.com>
On 2023-08-23 15:21, Niklas Schnelle wrote:
[...]
>>> +struct dma_iommu_options {
>>> +#define IOMMU_DMA_OPTS_PER_CPU_QUEUE 0L
>>
>> Nit: if the intent is to add more flags then that will no longer make
>> sense, and if not then we may as well just have a bool ;)
>>
>>> +#define IOMMU_DMA_OPTS_SINGLE_QUEUE BIT(0)
>
> My thinking was that the above two options are mutually exclusive with
> per-CPU encoded as BIT(0) unset and single queue as set. Then other
> options could still use the other bits. It's true though that the below
> use of IOMMU_DMA_OPTS_PER_CPU_QUEUE is a nop so maybe just drop that?
> Or we could use an enum even if I don't forsee more than these 2 queue
> types.
My point was that the value 0 can only mean "all flags not set", so
while we can very much have the semantic of "single queue flag not set
means percpu queue", we cannot infer "0 means percpu queue" unless "all
flags" and "single queue flag" are the same thing. As soon as any
additional flag is defined, 0 then has a different meaning which may
well not even be a combination that's useful to put a specific name to.
I'd like to hope it's sufficiently obvious from the implementation that
the opposite of a single queue is multiple queues, since contextually
this is already all happening in distinct paths from the case of no queue.
Thanks,
Robin.
next prev parent reply other threads:[~2023-08-29 15:39 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-17 11:00 [PATCH v11 0/6] iommu/dma: s390 DMA API conversion and optimized IOTLB flushing Niklas Schnelle
2023-07-17 11:00 ` [PATCH v11 1/6] iommu: Allow .iotlb_sync_map to fail and handle s390's -ENOMEM return Niklas Schnelle
2023-07-17 11:00 ` [PATCH v11 2/6] s390/pci: prepare is_passed_through() for dma-iommu Niklas Schnelle
2023-07-17 11:00 ` [PATCH v11 3/6] s390/pci: Use dma-iommu layer Niklas Schnelle
2023-07-17 11:00 ` [PATCH v11 4/6] iommu/s390: Force ISM devices to use IOMMU_DOMAIN_DMA Niklas Schnelle
2023-07-19 12:56 ` Matthew Rosato
2023-08-18 19:10 ` Robin Murphy
2023-08-23 10:53 ` Niklas Schnelle
2023-07-17 11:00 ` [PATCH v11 5/6] iommu/dma: Allow a single FQ in addition to per-CPU FQs Niklas Schnelle
2023-08-18 18:16 ` Robin Murphy
2023-08-23 14:21 ` Niklas Schnelle
2023-08-29 15:39 ` Robin Murphy [this message]
2023-07-17 11:00 ` [PATCH v11 6/6] iommu/dma: Use a large flush queue and timeout for shadow_on_flush Niklas Schnelle
2023-08-18 19:06 ` Robin Murphy
2023-08-18 16:51 ` [PATCH v11 0/6] iommu/dma: s390 DMA API conversion and optimized IOTLB flushing Jason Gunthorpe
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