linux-kernel - Re: [PATCH 00/10] Make PCI's devres API more consistent

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Date: Tue, 16 Jan 2024 23:17:23 +0200
From: andy.shevchenko@...il.com
To: Philipp Stanner <pstanner@...hat.com>
Cc: Jonathan Corbet <corbet@....net>, Hans de Goede <hdegoede@...hat.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Sam Ravnborg <sam@...nborg.org>, dakr@...hat.com,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 00/10] Make PCI's devres API more consistent

Mon, Jan 15, 2024 at 03:46:11PM +0100, Philipp Stanner kirjoitti:
> ¡Hola!

i? Vim user? :-)

> PCI's devres API suffers several weaknesses:
> 
> 1. There are functions prefixed with pcim_. Those are always managed
>    counterparts to never-managed functions prefixed with pci_ – or so one
>    would like to think. There are some apparently unmanaged functions
>    (all region-request / release functions, and pci_intx()) which
>    suddenly become managed once the user has initialized the device with
>    pcim_enable_device() instead of pci_enable_device(). This "sometimes
>    yes, sometimes no" nature of those functions is confusing and
>    therefore bug-provoking. In fact, it has already caused a bug in DRM.
>    The last patch in this series fixes that bug.
> 2. iomappings: Instead of giving each mapping its own callback, the
>    existing API uses a statically allocated struct tracking one mapping
>    per bar. This is not extensible. Especially, you can't create
>    _ranged_ managed mappings that way, which many drivers want.
> 3. Managed request functions only exist as "plural versions" with a
>    bit-mask as a parameter. That's quite over-engineered considering
>    that each user only ever mapps one, maybe two bars.
> 
> This series:
> - add a set of new "singular" devres functions that use devres the way
>   its intended, with one callback per resource.
> - deprecates the existing iomap-table mechanism.
> - deprecates the hybrid nature of pci_ functions.
> - preserves backwards compatibility so that drivers using the existing
>   API won't notice any changes.
> - adds documentation, especially some warning users about the
>   complicated nature of PCI's devres.

Instead of adding pcim_intx(), please provide proper one for
pci_alloc_irq_vectors(). Ideally it would be nice to deprecate
old IRQ management functions in PCI core and delete them in the
future.

-- 
With Best Regards,
Andy Shevchenko