linux-kernel - Re: [PATCH] PCI: designware: comment the condition of programming ATU in host init

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Date:	Thu, 4 Feb 2016 14:37:55 -0600
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	jingoohan1@...il.com, pratyush.anand@...il.com,
	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] PCI: designware: comment the condition of programming
 ATU in host init

On Thu, Jan 07, 2016 at 02:12:38PM +0800, Jisheng Zhang wrote:
> Some platforms don't support ATU, e.g pci-keystone.c, these platforms
> use their own address translation component rather than ATU, and they
> provide the rd_other_conf and wr_other_conf to programming the
> translation component then do the required access, so we ignore the ATU
> programming for these platforms. Add the comment to explain the reason.
> 
> As Bjorn pointed out,
> 
>   "these definitions:
> 
>   #define PCIE_ATU_TYPE_MEM
>   #define PCIE_ATU_TYPE_IO
>   #define PCIE_ATU_TYPE_CFG0
>   #define PCIE_ATU_TYPE_CFG1
> 
>   and these uses:
> 
>   - In dw_pcie_host_init(), set PCIE_ATU_TYPE_MEM for unit 1
>     (but only if rd_other_conf is not overridden)
> 
>   - In dw_pcie_rd_other_conf() and dw_pcie_wr_other_conf(),
>     set PCIE_ATU_TYPE_CFG0 before config access to own bus;
>     set PCIE_ATU_TYPE_CFG1 before config access to other bus;
>     set PCIE_ATU_TYPE_IO after completion
> 
>    Why is that initialization related to rd_other_conf?  Shouldn't that
>    be set up always?  A comment here would be nice..."
> 
> To be honest, I can't answer this question immediately until I read the
> code carefully again. So indeed, the comment is really necessary.
> 
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>

Applied to pci/host-designware for v4.6, thanks, Jisheng!

> ---
>  drivers/pci/host/pcie-designware.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/host/pcie-designware.c b/drivers/pci/host/pcie-designware.c
> index 02a7452..b795b20 100644
> --- a/drivers/pci/host/pcie-designware.c
> +++ b/drivers/pci/host/pcie-designware.c
> @@ -517,6 +517,12 @@ int dw_pcie_host_init(struct pcie_port *pp)
>  	if (pp->ops->host_init)
>  		pp->ops->host_init(pp);
>  
> +	/*
> +	 * If the platform provides ->rd_other_conf, it means the platform
> +	 * doesn't support ATU, it uses its own address translation component
> +	 * rather than ATU, so we should ignore ATU programming for this
> +	 * kind of platform.
> +	 */
>  	if (!pp->ops->rd_other_conf)
>  		dw_pcie_prog_outbound_atu(pp, PCIE_ATU_REGION_INDEX1,
>  					  PCIE_ATU_TYPE_MEM, pp->mem_base,
> -- 
> 2.7.0.rc3
> 
> --
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