Re: [PATCH] PCI: rcar: Always allocate MSI addresses in 32bit space

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Oct 16, 2020 at 02:04:31PM +0200, marek.vasut@gmail.com wrote:
> From: Marek Vasut <marek.vasut+renesas@gmail.com>
> 
> This fixes MSI operation on legacy PCI cards, which cannot issue 64bit MSIs.
> The R-Car controller only has one MSI trigger address instead of two, one
> for 64bit and one for 32bit MSI, set the address to 32bit PCIe space so that
> legacy PCI cards can also trigger MSIs.
> 
> Fixes: 290c1fb35860 ("PCI: rcar: Add MSI support for PCIe")
> Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Cc: Wolfram Sang <wsa@the-dreams.de>
> Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> Cc: linux-renesas-soc@vger.kernel.org
> ---
>  drivers/pci/controller/pcie-rcar-host.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-rcar-host.c b/drivers/pci/controller/pcie-rcar-host.c
> index 1194d5f3341b..ac5c7d7573a6 100644
> --- a/drivers/pci/controller/pcie-rcar-host.c
> +++ b/drivers/pci/controller/pcie-rcar-host.c
> @@ -753,7 +753,7 @@ static int rcar_pcie_enable_msi(struct rcar_pcie_host *host)
>  	}
>  
>  	/* setup MSI data target */
> -	msi->pages = __get_free_pages(GFP_KERNEL, 0);
> +	msi->pages = __get_free_pages(GFP_KERNEL | GFP_DMA32, 0);

This does not do what you want on !CONFIG_ZONE_DMA32 (ie arm LPAE).

Can't you just pick up a non-DMA-able address < 4GB (ie outside the host
controller inbound window range) and use it as doorbell address instead ?

Thanks,
Lorenzo

>  	rcar_pcie_hw_enable_msi(host);
>  
>  	return 0;
> -- 
> 2.28.0
>