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Date:   Sun, 9 Oct 2022 15:36:32 +0200
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Subject: Re: [PATCH v2] PCI: Assign PCI domain by ida_alloc()
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To:     =?UTF-8?Q?Pali_Roh=c3=a1r?= <pali@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Rob Herring <robh+dt@kernel.org>, Andrew Lunn <andrew@lunn.ch>,
        =?UTF-8?Q?Marek_Beh=c3=ban?= <marek.behun@nic.cz>
Cc:     linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20220702204737.7719-1-pali@kernel.org>
 <20220714184130.5436-1-pali@kernel.org>
From:   Christophe JAILLET <christophe.jaillet@wanadoo.fr>
In-Reply-To: <20220714184130.5436-1-pali@kernel.org>
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Le 14/07/2022 à 20:41, Pali Rohár a écrit :
> Replace assignment of PCI domain from atomic_inc_return() to ida_alloc().
> 
> Use two IDAs, one for static domain allocations (those which are defined in
> device tree) and second for dynamic allocations (all other).
> 
> During removal of root bus / host bridge release also allocated domain id.
> So released id can be reused again, for example in situation when
> dynamically loading and unloading native PCI host bridge drivers.
> 
> This change also allows to mix static device tree assignment and dynamic by
> kernel as all static allocations are reserved in dynamic pool.
> 

Hi,

A few comments below related to error handling.
Take them as a naive review from s.o. with limited knowledge of PCI ;-)

CJ

> Signed-off-by: Pali Rohár <pali@kernel.org>
> ---
> Idea of this patch comes from the following discussion:
> https://lore.kernel.org/linux-pci/20210412123936.25555-1-pali@kernel.org/t/#u
> 
> Changes in v2:
> * Fix broken compilation
> ---
>   drivers/pci/pci.c    | 103 +++++++++++++++++++++++++------------------
>   drivers/pci/probe.c  |   5 +++
>   drivers/pci/remove.c |   6 +++
>   include/linux/pci.h  |   1 +
>   4 files changed, 72 insertions(+), 43 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index cfaf40a540a8..34fdcee6634a 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6762,60 +6762,70 @@ static void pci_no_domains(void)
>   }
>   
>   #ifdef CONFIG_PCI_DOMAINS_GENERIC
> -static atomic_t __domain_nr = ATOMIC_INIT(-1);
> +static DEFINE_IDA(pci_domain_nr_static_ida);
> +static DEFINE_IDA(pci_domain_nr_dynamic_ida);
>   
> -static int pci_get_new_domain_nr(void)
> +static void of_pci_reserve_static_domain_nr(void)
>   {
> -	return atomic_inc_return(&__domain_nr);
> +	struct device_node *np;
> +	int domain_nr;
> +
> +	for_each_node_by_type(np, "pci") {
> +		domain_nr = of_get_pci_domain_nr(np);
> +		if (domain_nr < 0)
> +			continue;
> +		/*
> +		 * Permanently allocate domain_nr in dynamic_ida
> +		 * to prevent it from dynamic allocation.
> +		 */
> +		ida_alloc_range(&pci_domain_nr_dynamic_ida,
> +				domain_nr, domain_nr, GFP_KERNEL);

IIUC, if the DT is broken, 'domain_nr' could have several times the same 
value. In such a case ida_alloc_range() would return -ENOSPC.

Should this be handled here, maybe at least with a error message?

> +	}
>   }
>   
>   static int of_pci_bus_find_domain_nr(struct device *parent)
>   {
> -	static int use_dt_domains = -1;
> -	int domain = -1;
> +	static bool static_domains_reserved = false;
> +	int domain_nr;
>   
> -	if (parent)
> -		domain = of_get_pci_domain_nr(parent->of_node);
> +	/* On the first call scan device tree for static allocations. */
> +	if (!static_domains_reserved) {
> +		of_pci_reserve_static_domain_nr();
> +		static_domains_reserved = true;
> +	}
> +
> +	if (parent) {
> +		/*
> +		 * If domain is in DT then allocate it in static IDA.
> +		 * This prevent duplicate static allocations in case
> +		 * of errors in DT.
> +		 */
> +		domain_nr = of_get_pci_domain_nr(parent->of_node);
> +		if (domain_nr >= 0)
> +			return ida_alloc_range(&pci_domain_nr_static_ida,
> +					       domain_nr, domain_nr,
> +					       GFP_KERNEL);

Same here. Can ida_alloc_range() fail with -ENOSPC?
If yes, what should be done in such a case?

> +	}
>   
>   	/*
> -	 * Check DT domain and use_dt_domains values.
> -	 *
> -	 * If DT domain property is valid (domain >= 0) and
> -	 * use_dt_domains != 0, the DT assignment is valid since this means
> -	 * we have not previously allocated a domain number by using
> -	 * pci_get_new_domain_nr(); we should also update use_dt_domains to
> -	 * 1, to indicate that we have just assigned a domain number from
> -	 * DT.
> -	 *
> -	 * If DT domain property value is not valid (ie domain < 0), and we
> -	 * have not previously assigned a domain number from DT
> -	 * (use_dt_domains != 1) we should assign a domain number by
> -	 * using the:
> -	 *
> -	 * pci_get_new_domain_nr()
> -	 *
> -	 * API and update the use_dt_domains value to keep track of method we
> -	 * are using to assign domain numbers (use_dt_domains = 0).
> -	 *
> -	 * All other combinations imply we have a platform that is trying
> -	 * to mix domain numbers obtained from DT and pci_get_new_domain_nr(),
> -	 * which is a recipe for domain mishandling and it is prevented by
> -	 * invalidating the domain value (domain = -1) and printing a
> -	 * corresponding error.
> +	 * If domain was not specified in DT then choose free id from dynamic
> +	 * allocations. All domain numbers from DT are permanently in dynamic
> +	 * allocations to prevent assigning them to other DT nodes without
> +	 * static domain.
>   	 */
> -	if (domain >= 0 && use_dt_domains) {
> -		use_dt_domains = 1;
> -	} else if (domain < 0 && use_dt_domains != 1) {
> -		use_dt_domains = 0;
> -		domain = pci_get_new_domain_nr();
> -	} else {
> -		if (parent)
> -			pr_err("Node %pOF has ", parent->of_node);
> -		pr_err("Inconsistent \"linux,pci-domain\" property in DT\n");
> -		domain = -1;
> -	}
> +	return ida_alloc(&pci_domain_nr_dynamic_ida, GFP_KERNEL);

Same here, even if un-likelly.


> +}
>   
> -	return domain;
> +static void of_pci_bus_release_domain_nr(struct pci_bus *bus, struct device *parent)
> +{
> +	if (bus->domain_nr < 0)
> +		return;
> +
> +	/* Release domain from ida in which was it allocated. */
> +	if (of_get_pci_domain_nr(parent->of_node) == bus->domain_nr)
> +		ida_free(&pci_domain_nr_static_ida, bus->domain_nr);
> +	else
> +		ida_free(&pci_domain_nr_dynamic_ida, bus->domain_nr);
>   }
>   
>   int pci_bus_find_domain_nr(struct pci_bus *bus, struct device *parent)
> @@ -6823,6 +6833,13 @@ int pci_bus_find_domain_nr(struct pci_bus *bus, struct device *parent)
>   	return acpi_disabled ? of_pci_bus_find_domain_nr(parent) :
>   			       acpi_pci_bus_find_domain_nr(bus);
>   }
> +
> +void pci_bus_release_domain_nr(struct pci_bus *bus, struct device *parent)
> +{
> +	if (!acpi_disabled)
> +		return;
> +	of_pci_bus_release_domain_nr(bus, parent);
> +}
>   #endif
>   
>   /**
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..12092d238403 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -906,6 +906,8 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>   		bus->domain_nr = pci_bus_find_domain_nr(bus, parent);
>   	else
>   		bus->domain_nr = bridge->domain_nr;
> +	if (bus->domain_nr < 0)
> +		goto free;
>   #endif
>   
>   	b = pci_find_bus(pci_domain_nr(bus), bridge->busnr);
> @@ -1030,6 +1032,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>   	device_del(&bridge->dev);
>   
>   free:
> +#ifdef CONFIG_PCI_DOMAINS_GENERIC
> +	pci_bus_release_domain_nr(bus, parent);
> +#endif
>   	kfree(bus);
>   	return err;
>   }
> diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> index 4c54c75050dc..0145aef1b930 100644
> --- a/drivers/pci/remove.c
> +++ b/drivers/pci/remove.c
> @@ -160,6 +160,12 @@ void pci_remove_root_bus(struct pci_bus *bus)
>   	pci_remove_bus(bus);
>   	host_bridge->bus = NULL;
>   
> +#ifdef CONFIG_PCI_DOMAINS_GENERIC
> +	/* Release domain_nr if it was dynamically allocated */
> +	if (host_bridge->domain_nr == PCI_DOMAIN_NR_NOT_SET)
> +		pci_bus_release_domain_nr(bus, host_bridge->dev.parent);
> +#endif
> +
>   	/* remove the host bridge */
>   	device_del(&host_bridge->dev);
>   }
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 81a57b498f22..6c7f27e62bcc 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1723,6 +1723,7 @@ static inline int acpi_pci_bus_find_domain_nr(struct pci_bus *bus)
>   { return 0; }
>   #endif
>   int pci_bus_find_domain_nr(struct pci_bus *bus, struct device *parent);
> +void pci_bus_release_domain_nr(struct pci_bus *bus, struct device *parent);
>   #endif
>   
>   /* Some architectures require additional setup to direct VGA traffic */