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

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Message-ID: <b3fef8c7-29d2-e1d3-09c9-7bb97510faf0@arm.com>
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.