linux-kernel - Re: [PATCH v2] of/irq: Support #msi-cells=<0> in of_msi_get

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Message-ID: <CAL_Jsq+0fXJarCjLA1ZYOiHbM_qn3dtG00Xz+Z8qGCg8Wu=dgA@mail.gmail.com>
Date: Fri, 16 Aug 2024 14:18:41 -0600
From: Rob Herring <robh@...nel.org>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
	loongarch@...ts.linux.dev, linux-mips@...r.kernel.org, maz@...nel.org, 
	mark.rutland@....com, saravanak@...gle.com, paul.walmsley@...ive.com, 
	palmer@...belt.com, aou@...s.berkeley.edu, 
	Anup Patel <apatel@...tanamicro.com>
Subject: Re: [PATCH v2] of/irq: Support #msi-cells=<0> in of_msi_get_domain

On Fri, Aug 16, 2024 at 6:50 AM Andrew Jones <ajones@...tanamicro.com> wrote:
>
> An 'msi-parent' property with a single entry and no accompanying
> '#msi-cells' property is considered the legacy definition as opposed
> to its definition after being expanded with commit 126b16e2ad98
> ("Docs: dt: add generic MSI bindings"). However, the legacy
> definition is completely compatible with the current definition and,
> since of_phandle_iterator_next() tolerates missing and present-but-
> zero *cells properties since commit e42ee61017f5 ("of: Let
> of_for_each_phandle fallback to non-negative cell_count"), there's no
> need anymore to special case the legacy definition in
> of_msi_get_domain().
>
> Indeed, special casing has turned out to be harmful, because, as of
> commit 7c025238b47a ("dt-bindings: irqchip: Describe the IMX MU block
> as a MSI controller"), MSI controller DT bindings have started
> specifying '#msi-cells' as a required property (even when the value
> must be zero) as an effort to make the bindings more explicit. But,
> since the special casing of 'msi-parent' only uses the existence of
> '#msi-cells' for its heuristic, and not whether or not it's also
> nonzero, the legacy path is not taken. Furthermore, the path to
> support the new, broader definition isn't taken either since that
> path has been restricted to the platform-msi bus.
>
> But, neither the definition of 'msi-parent' nor the definition of
> '#msi-cells' is platform-msi-specific (the platform-msi bus was just
> the first bus that needed '#msi-cells'), so remove both the special
> casing and the restriction. The code removal also requires changing
> to of_parse_phandle_with_optional_args() in order to ensure the
> legacy (but compatible) use of 'msi-parent' remains supported. This
> not only simplifies the code but also resolves an issue with PCI
> devices finding their MSI controllers on riscv, as the riscv,imsics
> binding requires '#msi-cells=<0>'.
>
> Signed-off-by: Andrew Jones <ajones@...tanamicro.com>
> ---
> v2:
>  - switch to of_parse_phandle_with_optional_args() to ensure the
>    absence of #msi-cells means count=0
>
>  drivers/of/irq.c | 37 +++++++++++--------------------------
>  1 file changed, 11 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/of/irq.c b/drivers/of/irq.c
> index c94203ce65bb..690df4b71ab9 100644
> --- a/drivers/of/irq.c
> +++ b/drivers/of/irq.c
> @@ -709,8 +709,7 @@ struct irq_domain *of_msi_map_get_device_domain(struct device *dev, u32 id,
>   * @np: device node for @dev
>   * @token: bus type for this domain
>   *
> - * Parse the msi-parent property (both the simple and the complex
> - * versions), and returns the corresponding MSI domain.
> + * Parse the msi-parent property and returns the corresponding MSI domain.
>   *
>   * Returns: the MSI domain for this device (or NULL on failure).
>   */
> @@ -718,33 +717,19 @@ struct irq_domain *of_msi_get_domain(struct device *dev,
>                                      struct device_node *np,
>                                      enum irq_domain_bus_token token)
>  {
> -       struct device_node *msi_np;
> +       struct of_phandle_args args;
>         struct irq_domain *d;
> +       int index = 0;
>
> -       /* Check for a single msi-parent property */
> -       msi_np = of_parse_phandle(np, "msi-parent", 0);
> -       if (msi_np && !of_property_read_bool(msi_np, "#msi-cells")) {
> -               d = irq_find_matching_host(msi_np, token);
> -               if (!d)
> -                       of_node_put(msi_np);
> -               return d;
> -       }
> -
> -       if (token == DOMAIN_BUS_PLATFORM_MSI) {
> -               /* Check for the complex msi-parent version */
> -               struct of_phandle_args args;
> -               int index = 0;
> +       while (!of_parse_phandle_with_optional_args(np, "msi-parent",
> +                                                   "#msi-cells",
> +                                                   index, &args)) {

I guess you just maintained essentially what was here, but
of_for_each_phandle() should work here. It's a bit more efficient too
because of_parse_phandle_with_optional_args() is implemented using
of_for_each_phandle().

Rob