Re: [PATCH 2/2] PCI: tegra: Implement ->add_bus() callback

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Nov 23, 2015 at 01:40:26PM +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> The configuration space mapping on Tegra is somewhat special, and in

It'd be nice to have a tiny hint about specifically what is special
about Tegra config space mapping.

> order to avoid wasting virtual address space the configuration space
> for each bus needs to be stitched together from several blocks which
> form a single continuous virtual address range for accessors.
> 
> Currently the configuration space is mapped upon the first access to
> one of its registers. However, the mapping operation may sleep under
> certain circumstances, so doing it from the configuration space
> accessors (they are protected by a spin lock) will trigger a warning.

Can you include the exact warning?  Does it happen always?  Always on
the first config access to a bus?

> To avoid the warning, use the ->add_bus() callback to perform the
> mapping at enumeration time when the operation is allowed to sleep.
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/pci/host/pci-tegra.c | 40 +++++++++++++++++++---------------------
>  1 file changed, 19 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/pci/host/pci-tegra.c b/drivers/pci/host/pci-tegra.c
> index 3018ae52e092..c3666f9d7ef1 100644
> --- a/drivers/pci/host/pci-tegra.c
> +++ b/drivers/pci/host/pci-tegra.c
> @@ -426,31 +426,23 @@ free:
>  	return ERR_PTR(err);
>  }
>  
> -/*
> - * Look up a virtual address mapping for the specified bus number. If no such
> - * mapping exists, try to create one.
> - */
> -static void __iomem *tegra_pcie_bus_map(struct tegra_pcie *pcie,
> -					unsigned int busnr)
> +static int tegra_pcie_add_bus(struct pci_bus *bus)
>  {
> -	struct tegra_pcie_bus *bus;
> +	struct tegra_pcie *pcie = sys_to_pcie(bus->sysdata);
> +	struct tegra_pcie_bus *b;
>  
> -	list_for_each_entry(bus, &pcie->buses, list)
> -		if (bus->nr == busnr)
> -			return (void __iomem *)bus->area->addr;
> +	b = tegra_pcie_bus_alloc(pcie, bus->number);
> +	if (IS_ERR(b))
> +		return PTR_ERR(b);
>  
> -	bus = tegra_pcie_bus_alloc(pcie, busnr);
> -	if (IS_ERR(bus))
> -		return NULL;
> +	list_add_tail(&b->list, &pcie->buses);
>  
> -	list_add_tail(&bus->list, &pcie->buses);
> -
> -	return (void __iomem *)bus->area->addr;
> +	return 0;
>  }
>  
> -static void __iomem *tegra_pcie_conf_address(struct pci_bus *bus,
> -					     unsigned int devfn,
> -					     int where)
> +static void __iomem *tegra_pcie_map_bus(struct pci_bus *bus,
> +					unsigned int devfn,
> +					int where)
>  {
>  	struct tegra_pcie *pcie = sys_to_pcie(bus->sysdata);
>  	void __iomem *addr = NULL;
> @@ -466,7 +458,12 @@ static void __iomem *tegra_pcie_conf_address(struct pci_bus *bus,
>  			}
>  		}
>  	} else {
> -		addr = tegra_pcie_bus_map(pcie, bus->number);
> +		struct tegra_pcie_bus *b;
> +
> +		list_for_each_entry(b, &pcie->buses, list)
> +			if (b->nr == bus->number)
> +				addr = (void __iomem *)b->area->addr;
> +
>  		if (!addr) {
>  			dev_err(pcie->dev,
>  				"failed to map cfg. space for bus %u\n",
> @@ -481,7 +478,8 @@ static void __iomem *tegra_pcie_conf_address(struct pci_bus *bus,
>  }
>  
>  static struct pci_ops tegra_pcie_ops = {
> -	.map_bus = tegra_pcie_conf_address,
> +	.add_bus = tegra_pcie_add_bus,
> +	.map_bus = tegra_pcie_map_bus,
>  	.read = pci_generic_config_read32,
>  	.write = pci_generic_config_write32,
>  };
> -- 
> 2.5.0
> 
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