linux-kernel - Re: [PATCH] PCI: j721e: Set .map_irq and .swizzle

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Message-ID: <20240725074708.GB2770@thinkpad>
Date: Thu, 25 Jul 2024 13:17:08 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Siddharth Vadapalli <s-vadapalli@...com>
Cc: bhelgaas@...gle.com, lpieralisi@...nel.org, kw@...ux.com,
	robh@...nel.org, vigneshr@...com, kishon@...nel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org,
	ahalaney@...hat.com, srk@...com
Subject: Re: [PATCH] PCI: j721e: Set .map_irq and .swizzle_irq to NULL

On Thu, Jul 25, 2024 at 10:50:13AM +0530, Siddharth Vadapalli wrote:
> On Wed, Jul 24, 2024 at 09:49:16PM +0530, Manivannan Sadhasivam wrote:
> > On Wed, Jul 24, 2024 at 12:20:48PM +0530, Siddharth Vadapalli wrote:
> > > Since the configuration of Legacy Interrupts (INTx) is not supported, set
> > > the .map_irq and .swizzle_irq callbacks to NULL. This fixes the error:
> > >   of_irq_parse_pci: failed with rc=-22
> > > due to the absence of Legacy Interrupts in the device-tree.
> > > 
> > 
> > Do you really need to set 'swizzle_irq' to NULL? pci_assign_irq() will bail out
> > if 'map_irq' is set to NULL.
> 
> While 'swizzle_irq' won't be invoked if 'map_irq' is NULL, having a
> non-NULL 'swizzle_irq' (pci_common_swizzle in this case) with a NULL
> 'map_irq' seems inconsistent to me though the code-path may never invoke
> it. Wouldn't a non-NULL 'swizzle_irq' imply that Legacy Interrupts are
> supported, while a NULL 'map_irq' indicates that they aren't? Since they
> are always described in pairs, whether it is in the initial commit that
> added support for the Cadence PCIe Host controller (used by pci-j721e.c):
> https://github.com/torvalds/linux/commit/1b79c5284439
> OR the commit which moved the shared 'map_irq' and 'swizzle_irq' defaults
> from all the host drivers into the common 'devm_of_pci_bridge_init()'
> function:
> https://github.com/torvalds/linux/commit/b64aa11eb2dd
> I have set both of them to NULL for the sake of consistency.
> 

Since both callbacks are populated in the pci/of driver, this consistency won't
be visible in the controller drivers. From the functionality pov, setting both
callbacks to NULL is *not* required to disable INTx, right?

- Mani

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