Re: [PATCH 1/7] irqchip/gic-v3: Add a DMA Non-Coherent flag

From: Marc Zyngier <maz@kernel.org>
To: Lucas Tanure <lucas.tanure@collabora.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
	Peter Geis <pgwipeout@gmail.com>, Vinod Koul <vkoul@kernel.org>,
	Kishon Vijay Abraham I <kishon@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Heiko Stuebner <heiko@sntech.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Krzysztof Wilczynski <kw@linux.com>,
	Bjorn Helgaas <bhelgaas@google.com>, Qu Wenruo <wqu@suse.com>,
	Piotr Oniszczuk <piotr.oniszczuk@gmail.com>,
	Kever Yang <kever.yang@rock-chips.com>,
	linux-phy@lists.infradead.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, kernel@collabora.com
Subject: Re: [PATCH 1/7] irqchip/gic-v3: Add a DMA Non-Coherent flag
Date: Tue, 14 Mar 2023 14:14:27 +0000	[thread overview]
Message-ID: <86h6unxvwc.wl-maz@kernel.org> (raw)
In-Reply-To: <93e4d83d-9559-c987-d93b-c49572413275@collabora.com>

On Tue, 14 Mar 2023 13:25:28 +0000,
Lucas Tanure <lucas.tanure@collabora.com> wrote:
> 
> On 10-03-2023 12:04, Robin Murphy wrote:
> > On 2023-03-10 11:41, Peter Geis wrote:
> >> On Fri, Mar 10, 2023 at 3:05 AM Lucas Tanure
> >> <lucas.tanure@collabora.com> wrote:
> >>> 
> >>> The GIC600 integration in RK356x, used in rk3588, doesn't support
> >>> any of the shareability or cacheability attributes, and requires
> >>> both values to be set to 0b00 for all the ITS and Redistributor
> >>> tables.
> >>> 
> >>> This is loosely based on prior work from XiaoDong Huang and
> >>> Peter Geis fixing this issue specifically for Rockchip 356x.
> >> 
> >> Good Morning,
> >> 
> >> Since the gic is using dma, would it be reasonable to have all memory
> >> allocations be requested with the GFP_DMA flag? Otherwise this doesn't
> >> fully solve the problem for rk356x, where only the lower 4GB range is
> >> DMA capable, but this tends to get allocated in the upper 4GB on 8GB
> >> boards.
> > 
> > Not really, because there's no fixed definition of what GFP_DMA
> > actually means, and it may mean nothing (same for GFP_DMA32, which
> > may or may not be meaningful depending on kernel config and platform
> > topology). Drivers should really use the DMA API allocation
> > functions if they care about what they get, which comes back round
> > to the notion from years ago of converting the ITS driver to a
> > regular platform driver, so it can benefit from regular DT concepts
> > like "dma-ranges" automatically.
> > 
> > Thanks,
> > Robin.
> > 
> I am looking how to do that conversion to platform driver.
> But about the communication between irq-gic-v3-its and irq-gic-v3.
> Should irq-gic-v3-its be a MFD child of irq-gic-v3?

MFD? I'd rather suggest an VME bus driver. ;-)

Seriously, this is an interrupt controller. Nothing else. It should
probe the parent irqdomain, and stack onto that. No parent? Probe
deferral.

> Or use the component bind/unbind framework?

I don't understand what you mean here.

	M.

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

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