linux-kernel - [PATCH v2 09/10] gpio: Update TODO to mention immutable irq

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Date:   Tue,  5 Apr 2022 14:54:43 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Thierry Reding <thierry.reding@...il.com>,
        Joey Gouly <joey.gouly@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Basavaraj Natikar <Basavaraj.Natikar@....com>,
        Shyam Sundar S K <Shyam-sundar.S-k@....com>,
        linux-gpio@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, kernel-team@...roid.com
Subject: [PATCH v2 09/10] gpio: Update TODO to mention immutable irq_chip structures

5 drivers are converted, a few hundred to go. Definitely worth of
a TODO entry, in the hope that someone will notice it and do
a bulk update.

Signed-off-by: Marc Zyngier <maz@...nel.org>
---
 drivers/gpio/TODO | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpio/TODO b/drivers/gpio/TODO
index b8b1473a5b1e..f87ff3fa8a53 100644
--- a/drivers/gpio/TODO
+++ b/drivers/gpio/TODO
@@ -178,3 +178,22 @@ discussed but the idea is to provide a low-level access point
 for debugging and hacking and to expose all lines without the
 need of any exporting. Also provide ample ammunition to shoot
 oneself in the foot, because this is debugfs after all.
+
+
+Moving over to immutable irq_chip structures
+
+Most of the gpio chips implementing interrupt support rely on gpiolib
+intercepting some of the irq_chip callbacks, preventing the structures
+from being made read-only and forcing duplication of structures that
+should otherwise be unique.
+
+The solution is to call into the gpiolib code when needed (resource
+management, enable/disable or unmask/mask callbacks), and to let the
+core code know about that by exposing a flag (IRQCHIP_IMMUTABLE) in
+the irq_chip structure. The irq_chip structure can then be made unique
+and const.
+
+A small number of drivers have been converted (pl061, tegra186, msm,
+amd, apple), and can be used as examples of how to proceed with this
+conversion. Note that drivers using the generic irqchip framework
+cannot be converted yet, but watch this space!
-- 
2.34.1