linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: Add a configurable tlbi_range_max_n

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Message-ID: <ZN0CciT2hBISXxoJ@Asurada-Nvidia>
Date:   Wed, 16 Aug 2023 10:09:20 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     <will@...nel.org>, <robin.murphy@....com>, <joro@...tes.org>,
        <jean-philippe@...aro.org>, <apopple@...dia.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>
Subject: Re: [PATCH] iommu/arm-smmu-v3: Add a configurable
 tlbi_range_max_n_shift for TLBI

On Wed, Aug 16, 2023 at 08:59:59AM -0300, Jason Gunthorpe wrote:
> On Mon, Aug 14, 2023 at 02:57:01PM -0700, Nicolin Chen wrote:
> > +static ssize_t tlbi_range_max_n_shift_show(struct device *dev,
> > +					   struct device_attribute *attr,
> > +					   char *buf)
> > +{
> > +	struct arm_smmu_device *smmu = dev_get_drvdata(dev->parent);
> > +
> > +	return sprintf(buf, "%u\n", smmu->tlbi_range_max_n_shift);
> > +}
> 
> sysfs_emit and missing newline

Will replace and add a new line.

> > +static ssize_t tlbi_range_max_n_shift_store(struct device *dev,
> > +					    struct device_attribute *attr,
> > +					    const char *buf, size_t size)
> > +{
> > +	struct arm_smmu_device *smmu = dev_get_drvdata(dev->parent);
> > +	unsigned int max_n_shift;
> > +	int ret;
> > +
> > +	ret = kstrtou32(buf, 0, &max_n_shift);
> > +	if (ret)
> > +		return ret;
> > +	if (max_n_shift > VA_BITS || max_n_shift < PAGE_SHIFT)
> > +		return -EINVAL;
> > +	smmu->tlbi_range_max_n_shift = max_n_shift;
> > +	return size;
> 
> This seems convoluted for a uapi, you should just make it
> 'invalidate_threshold' in bytes or something simpler.

Hmm. That'd be a direct 64-bit size configuration, and very likely
to be at upper 32-bit range, so I feel the value would be very big
that might be hard to read.

With that said, I can rename the uAPI, yet still keep the bitshift
configuration.

> > +static struct attribute_group arm_smmu_group = {
> > +	.name = "arm-smmu-v3",
> > +	.attrs = arm_smmu_attrs,
> > +};
> 
> Do we really need the subdirectory?

OK. Let me try unfolding it.

Thanks!
Nicolin