linux-kernel - Re: [PATCH v14 08/10] iommu/arm-smmu-v3: Add in-kernel support for NVIDIA Tegra241 (Grace) CMDQV

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Message-ID: <ZtibUr0dRdAL7DjU@Asurada-Nvidia>
Date: Wed, 4 Sep 2024 10:39:30 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
CC: <will@...nel.org>, <robin.murphy@....com>, <joro@...tes.org>,
	<jgg@...dia.com>, <thierry.reding@...il.com>, <vdumpa@...dia.com>,
	<jonathanh@...dia.com>, <linux-kernel@...r.kernel.org>,
	<iommu@...ts.linux.dev>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v14 08/10] iommu/arm-smmu-v3: Add in-kernel support for
 NVIDIA Tegra241 (Grace) CMDQV

On Wed, Sep 04, 2024 at 08:12:19PM +0300, Dan Carpenter wrote:
 
> On Wed, Sep 04, 2024 at 08:17:11AM -0700, Nicolin Chen wrote:
> > Hi Dan,
> >
> > On Wed, Sep 04, 2024 at 10:29:26AM +0300, Dan Carpenter wrote:
> >
> > > I was reviewing Smatch warnings:
> > >
> > >     drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c:616 tegra241_cmdqv_init_vintf()
> > >     error: Calling ida_alloc_max() with a 'max' argument which is a power of 2. -1 missing?
> > >
> > > The problem is that we're calling ida_alloc_max() where max is always zero.
> > >
> > > > +static int tegra241_cmdqv_init_vintf(struct tegra241_cmdqv *cmdqv, u16 max_idx,
> > > > +                                  struct tegra241_vintf *vintf)
> > > > +{
> > > > +
> > > > +     u16 idx;
> > > > +     int ret;
> > > > +
> > > > +     ret = ida_alloc_max(&cmdqv->vintf_ids, max_idx, GFP_KERNEL);
> > > > +     if (ret < 0)
> > > > +             return ret;
> > > > +     idx = ret;
> > >
> > > max_idx is always zero so idx is always zero.
> >
> > There is a followup series adding support for max[1, max_vintf].
> > And I guess that would make Smatch happy. I'd personally prefer
> > keep this by ignoring the Smatch warning. But if you think the
> > common practice is to drop it and add back, I'd be okay with it.
> >
> 
> I'm just reviewing static checker warnings so I don't know the back story...
> How long are we going to have to wait for the follow on patchset?

There are a couple of dependencies we need to get merged first.
So, it might take a few months I think.

Perhaps I can make a small patch by changing the ida_alloc_max
in the common place here to iad_alloc_range(.., 1, max,..) in
the caller of the followup series. Then the existing caller for
vintf0 wouldn't need an ida_alloc().

> Generally if someone had noticed this in review they would have asked that it
> be dropped but now that it's in, you're probably in the clear.  No one else is
> going to volunteer to refactor this code if you don't.  ;)
> 
> With regards, to ignoring static checker warnings.  These are one time emails.
> There is always going to be a certain percent of false positives.  You're
> *encouraged* to ignore static checker warnings unless it's a bug or it makes the
> code cleaner.  The goal is never to silence the checker.

I see. Thanks for the note!

Nicolin