linux-kernel - Re: [PATCH 1/3] resource: Add resource set range and size helpers

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Date: Thu, 13 Jun 2024 14:28:20 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC: Bjorn Helgaas <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>, "Lorenzo
 Pieralisi" <lpieralisi@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof
 Wilczyński <kw@...ux.com>, <linux-kernel@...r.kernel.org>,
	Jonathan Hunter <jonathanh@...dia.com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	"Robert Richter" <rric@...nel.org>, Thierry Reding
	<thierry.reding@...il.com>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH 1/3] resource: Add resource set range and size helpers

On Wed, 12 Jun 2024 11:56:27 +0300
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:

> Setting the end address for a resource with a given size lacks a helper
> and is therefore open coded unlike the getter side which has a helper
> for resource size calculation. Also, almost all callsites that
> calculate end address for a resource also set the start address right
> before it like this:
> 
> 	res->start = start_addr;
> 	res->end = res->start + size - 1;
> 
> Thus, add resource_set_range(res, start_addr, size) that sets the start
> address and calculates the end address to simplify this often repeated
> fragment. In addition, introduce resource_set_size() for the cases
> where setting the start address of the resource is not necessary but
> note resource_set_range() is preferred.
> 
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

We have a bunch of cases of this in CXL. Adding this helper seems like
a good idea to me.

I'm not sure the odd semantics of resource_set_size() are a good idea.
Maybe it could by naming hint that it's relying internally on
size already being set.

resource_update_size() for instance might make people think or perhaps
that's just more obscure.  Meh, I've argued myself around to there
not being a better name.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>`


> ---
>  include/linux/ioport.h | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> index db7fe25f3370..2a1d33ad151c 100644
> --- a/include/linux/ioport.h
> +++ b/include/linux/ioport.h
> @@ -216,6 +216,38 @@ struct resource *lookup_resource(struct resource *root, resource_size_t start);
>  int adjust_resource(struct resource *res, resource_size_t start,
>  		    resource_size_t size);
>  resource_size_t resource_alignment(struct resource *res);
> +
> +/**
> + * resource_set_size - Calculates resource end address from size and start address
> + * @res: The resource descriptor
> + * @size: The size of the resource
> + *
> + * Calculates the end address for @res based on @size.
> + *
> + * Note: The start address of @res must be set when calling this function.
> + * Use resource_set_range() if setting both the start address and @size.
> + */
> +static inline void resource_set_size(struct resource *res, resource_size_t size)
> +{
> +	res->end = res->start + size - 1;
> +}
> +
> +/**
> + * resource_set_range - Sets resource start and end addresses
> + * @res: The resource descriptor
> + * @start: The start address for the resource
> + * @size: The size of the resource
> + *
> + * Sets @res start address and calculates the end address based on @size.
> + */
> +static inline void resource_set_range(struct resource *res,
> +				      resource_size_t start,
> +				      resource_size_t size)
> +{
> +	res->start = start;
> +	resource_set_size(res, size);
> +}
> +
>  static inline resource_size_t resource_size(const struct resource *res)
>  {
>  	return res->end - res->start + 1;