linux-kernel - Re: [PATCH v6 3/5] drm: handle HAS

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Message-Id: <c58ab639-f0de-4cea-b745-13e9cfe0e588@app.fastmail.com>
Date: Mon, 07 Oct 2024 14:50:11 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Lucas De Marchi" <lucas.demarchi@...el.com>,
 "Niklas Schnelle" <schnelle@...ux.ibm.com>
Cc: "Brian Cain" <bcain@...cinc.com>,
 "Marcel Holtmann" <marcel@...tmann.org>,
 "Luiz Augusto von Dentz" <luiz.dentz@...il.com>,
 "Patrik Jakobsson" <patrik.r.jakobsson@...il.com>,
 "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
 "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>,
 "Dave Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>,
 "Dave Airlie" <airlied@...hat.com>, "Gerd Hoffmann" <kraxel@...hat.com>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 "Rodrigo Vivi" <rodrigo.vivi@...el.com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Jiri Slaby" <jirislaby@...nel.org>,
 "Maciej W. Rozycki" <macro@...am.me.uk>,
 "Heiko Carstens" <hca@...ux.ibm.com>, linux-kernel@...r.kernel.org,
 linux-hexagon@...r.kernel.org, linux-bluetooth@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, virtualization@...ts.linux.dev,
 spice-devel@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
 linux-serial@...r.kernel.org, Linux-Arch <linux-arch@...r.kernel.org>,
 "Arnd Bergmann" <arnd@...nel.org>
Subject: Re: [PATCH v6 3/5] drm: handle HAS_IOPORT dependencies

On Mon, Oct 7, 2024, at 14:39, Lucas De Marchi wrote:
> as an example:
> $ git grep -lw outb -- drivers/gpu/drm/
> drivers/gpu/drm/gma500/cdv_device.c
> drivers/gpu/drm/i915/display/intel_vga.c
> drivers/gpu/drm/qxl/qxl_cmd.c
> drivers/gpu/drm/qxl/qxl_irq.c
> drivers/gpu/drm/tiny/bochs.c
> drivers/gpu/drm/tiny/cirrus.c
>
> you are adding the dependency on xe, but why are you keeping i915 out?
> What approach did you use to determine the dependency?

I did a lot of 'randconfig' build testing on earlier versions
(and this version) of the series, which eventually catches
all of them. The i915 driver depends on CONfIG_X86 since it
is only used in Intel PC chipsets that already rely on PIO.

The XE driver is also used for add-on cards, so the drivers
can be built on all architectures including those that do
not support PCI I/O space access. Adding the dependency on
i915 as well wouldn't be wrong, but is not required for
correctness.

I also sent a patch for vmwgfx, which can be used on arm64.
arm64 currently always sets HAS_IOPORT, so my patch is not
required as a dependency for [PATCH v6 5/5], but we eventually
want this so HAS_IOPORT can become optional on arm64.

      Arnd