linux-kernel - Re: [RFC PATCH] of/platform: Drop static setup of IRQ resource from DT core

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Message-ID: <87r170ydds.wl-maz@kernel.org>
Date:   Thu, 17 Mar 2022 12:25:35 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Prabhakar <prabhakar.csengg@...il.com>,
        linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [RFC PATCH] of/platform: Drop static setup of IRQ resource from DT core

On Wed, 16 Mar 2022 20:06:33 +0000,
Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com> wrote:
> 
> Now that all the DT drivers have switched to platform_get_irq() we can now
> safely drop the static setup of IRQ resource from DT core code.
> 
> With the above change hierarchical setup of irq domains is no longer
> bypassed and thus allowing hierarchical interrupt domains to describe
> interrupts using "interrupts" DT property.
> 
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> ---
> Hi All,
> 
> Sending this as RFC as couple of more drivers need to hit -rc yet with
> the platform_get_irq() change while that is in progress I wanted to get
> some feedback on this patch.
> 
> Cheers,
> Prabhakar
> ---
>  drivers/of/platform.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index 793350028906..6890f7fe556f 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -114,35 +114,31 @@ struct platform_device *of_device_alloc(struct device_node *np,
>  				  struct device *parent)
>  {
>  	struct platform_device *dev;
> -	int rc, i, num_reg = 0, num_irq;
> +	int rc, i, num_reg = 0;
>  	struct resource *res, temp_res;
>  
>  	dev = platform_device_alloc("", PLATFORM_DEVID_NONE);
>  	if (!dev)
>  		return NULL;
>  
> -	/* count the io and irq resources */
> +	/* count the io resources */
>  	while (of_address_to_resource(np, num_reg, &temp_res) == 0)
>  		num_reg++;
> -	num_irq = of_irq_count(np);
>  
>  	/* Populate the resource table */
> -	if (num_irq || num_reg) {
> -		res = kcalloc(num_irq + num_reg, sizeof(*res), GFP_KERNEL);
> +	if (num_reg) {
> +		res = kcalloc(num_reg, sizeof(*res), GFP_KERNEL);
>  		if (!res) {
>  			platform_device_put(dev);
>  			return NULL;
>  		}
>  
> -		dev->num_resources = num_reg + num_irq;
> +		dev->num_resources = num_reg;
>  		dev->resource = res;
>  		for (i = 0; i < num_reg; i++, res++) {
>  			rc = of_address_to_resource(np, i, res);
>  			WARN_ON(rc);
>  		}
> -		if (of_irq_to_resource_table(np, res, num_irq) != num_irq)
> -			pr_debug("not all legacy IRQ resources mapped for %pOFn\n",
> -				 np);
>  	}
>  
>  	dev->dev.of_node = of_node_get(np);

I think this definitely goes in the right direction by not eagerly
populating resources without a driver actually needing it. If anything
breaks, that should be seen as an opportunity to fix the users of this
misfeature. I booted a couple of boxes with this patch, and nothing
caught fire, so:

Acked-by: Marc Zyngier <maz@...nel.org>
Tested-by: Marc Zyngier <maz@...nel.org>

	M.

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