linux-kernel - Re: [PATCH v4 3/3] irqchip/gic-v3: Enable non-coherent redistributors/ITSes ACPI probing

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Date: Mon, 08 Jan 2024 09:52:20 +0000
From: Marc Zyngier <maz@...nel.org>
To: Lorenzo Pieralisi <lpieralisi@...nel.org>
Cc: linux-kernel@...r.kernel.org,
	Robin Murphy <robin.murphy@....com>,
	Mark Rutland <mark.rutland@....com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-acpi@...r.kernel.org,
	acpica-devel@...ts.linux.dev,
	Fang Xiang <fangxiang3@...omi.com>,
	Robert Moore <robert.moore@...el.com>
Subject: Re: [PATCH v4 3/3] irqchip/gic-v3: Enable non-coherent redistributors/ITSes ACPI probing

On Mon, 08 Jan 2024 09:43:23 +0000,
Lorenzo Pieralisi <lpieralisi@...nel.org> wrote:
> 
> On Thu, Jan 04, 2024 at 11:12:28AM +0000, Marc Zyngier wrote:
> > On Wed, 27 Dec 2023 11:00:38 +0000,
> > Lorenzo Pieralisi <lpieralisi@...nel.org> wrote:
> > > 
> > > The GIC architecture specification defines a set of registers
> > > for redistributors and ITSes that control the sharebility and
> > > cacheability attributes of redistributors/ITSes initiator ports
> > > on the interconnect (GICR_[V]PROPBASER, GICR_[V]PENDBASER,
> > > GITS_BASER<n>).
> > > 
> > > Architecturally the GIC provides a means to drive shareability
> > > and cacheability attributes signals and related IWB/OWB/ISH barriers
> > 
> > IWB/OWB *barriers*? Unless you're talking about something else,
> > IWB/OWB refers to cacheability, and only that.
> 
> Yes, it should be expressed differently. Unfortunately this sentence made
> it into the kernel with the DT counterpart - commit 3a0fff0fb6a3 log,
> apologies.

Oh well. At least please clean this one up when you repost.

[...]

> > > +	if (!madt_read) {
> > > +		madt_read = true;
> > 
> > Huh. Why do we need this hack? What's the issue with accessing the
> > MADT? Can it disappear from under our feet? While we're walking it?
> 
> It is an awkward attempt at stashing the revision instead of
> calling acpi_get_table() repeatedly (and from multiple files
> for the same reason - ie get an MADT rev number).
> 
> Side note: get_madt_table() does the same thing and I followed
> it - I am not sure it is very helpful either (or maybe
> there is something I don't know behind that reasoning).

This was introduced as part of 149fe9c293f76, as a cleanup. Not a
great move IMHO.

	M.

-- 
Without deviation from the norm, progress is not possible.