netdev - Re: [PATCH v9 5/6] iommu/dma: Allow a single FQ in addition to per-CPU FQs

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Date: Tue, 23 May 2023 13:16:40 +0100
From: Robin Murphy <robin.murphy@....com>
To: Niklas Schnelle <schnelle@...ux.ibm.com>, Joerg Roedel <joro@...tes.org>,
 Matthew Rosato <mjrosato@...ux.ibm.com>, Will Deacon <will@...nel.org>,
 Wenjia Zhang <wenjia@...ux.ibm.com>, Jason Gunthorpe <jgg@...pe.ca>
Cc: Gerd Bayer <gbayer@...ux.ibm.com>, Julian Ruess <julianr@...ux.ibm.com>,
 Pierre Morel <pmorel@...ux.ibm.com>, Alexandra Winter
 <wintera@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
 Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
 Alyssa Rosenzweig <alyssa@...enzweig.io>,
 David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>,
 Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>, Yong Wu <yong.wu@...iatek.com>,
 Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Orson Zhai <orsonzhai@...il.com>, Baolin Wang
 <baolin.wang@...ux.alibaba.com>, Chunyan Zhang <zhang.lyra@...il.com>,
 Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Samuel Holland <samuel@...lland.org>,
 Thierry Reding <thierry.reding@...il.com>, Krishna Reddy
 <vdumpa@...dia.com>, Jonathan Hunter <jonathanh@...dia.com>,
 Jonathan Corbet <corbet@....net>, linux-s390@...r.kernel.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
 asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org,
 linux-sunxi@...ts.linux.dev, linux-tegra@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCH v9 5/6] iommu/dma: Allow a single FQ in addition to
 per-CPU FQs

On 2023-05-23 13:02, Niklas Schnelle wrote:
[...]
>>> +static void fq_flush_single(struct iommu_dma_cookie *cookie)
>>> +{
>>> +	struct iova_fq *fq = cookie->single_fq;
>>> +	unsigned long flags;
>>> +
>>> +	spin_lock_irqsave(&fq->lock, flags);
>>> +	fq_ring_free(cookie, fq);
>>> +	spin_unlock_irqrestore(&fq->lock, flags)
>>
>> Nit: this should clearly just be a self-locked version of fq_ring_free()
>> that takes fq as an argument, then both the new case and the existing
>> loop body become trivial one-line calls.
> 
> Sure will do. Just one question about names. As an example
> pci_reset_function_locked() means that the relevant lock is already
> taken with pci_reset_function() adding the lock/unlock. In your wording
> the implied function names sound the other way around. I can't find
> anything similar in drivers/iommu so would you mind going the PCI way
> and having:
> 
> fq_ring_free_locked(): Called in queue_iova() with the lock held
> fr_ring_free(): Called in fq_flush_timeout() takes the lock itself
> 
> Or maybe I'm just biased because I've used the PCI ..locked() functions
> before and there is a better convention.

Yes, that's the form that's most familiar to me too - sorry I failed to 
express it clearly :)

Thanks,
Robin.