linux-kernel - Re: [PATCH v4 03/14] PCI: cadence: Add support to use custom read and write accessors

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Date:   Wed, 20 May 2020 16:07:24 -0600
From:   Rob Herring <robh@...nel.org>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Tom Joseph <tjoseph@...ence.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 03/14] PCI: cadence: Add support to use custom read
 and write accessors

On Wed, May 06, 2020 at 08:44:18PM +0530, Kishon Vijay Abraham I wrote:
> Add support to use custom read and write accessors. Platforms that
> don't support half word or byte access or any other constraint
> while accessing registers can use this feature to populate custom
> read and write accessors. These custom accessors are used for both
> standard register access and configuration space register access of
> the PCIe host bridge.
> 
> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/pci/controller/cadence/pcie-cadence.h | 107 +++++++++++++++---
>  1 file changed, 94 insertions(+), 13 deletions(-)

Actually, take back my R-by...

> 
> diff --git a/drivers/pci/controller/cadence/pcie-cadence.h b/drivers/pci/controller/cadence/pcie-cadence.h
> index df14ad002fe9..70b6b25153e8 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence.h
> +++ b/drivers/pci/controller/cadence/pcie-cadence.h
> @@ -223,6 +223,11 @@ enum cdns_pcie_msg_routing {
>  	MSG_ROUTING_GATHER,
>  };
>  
> +struct cdns_pcie_ops {
> +	u32	(*read)(void __iomem *addr, int size);
> +	void	(*write)(void __iomem *addr, int size, u32 value);
> +};
> +
>  /**
>   * struct cdns_pcie - private data for Cadence PCIe controller drivers
>   * @reg_base: IO mapped register base
> @@ -239,7 +244,7 @@ struct cdns_pcie {
>  	int			phy_count;
>  	struct phy		**phy;
>  	struct device_link	**link;
> -	const struct cdns_pcie_common_ops *ops;
> +	const struct cdns_pcie_ops *ops;
>  };
>  
>  /**
> @@ -299,69 +304,145 @@ struct cdns_pcie_ep {
>  /* Register access */
>  static inline void cdns_pcie_writeb(struct cdns_pcie *pcie, u32 reg, u8 value)
>  {
> -	writeb(value, pcie->reg_base + reg);
> +	void __iomem *addr = pcie->reg_base + reg;
> +
> +	if (pcie->ops && pcie->ops->write) {
> +		pcie->ops->write(addr, 0x1, value);
> +		return;
> +	}
> +
> +	writeb(value, addr);
>  }
>  
>  static inline void cdns_pcie_writew(struct cdns_pcie *pcie, u32 reg, u16 value)
>  {
> -	writew(value, pcie->reg_base + reg);
> +	void __iomem *addr = pcie->reg_base + reg;
> +
> +	if (pcie->ops && pcie->ops->write) {
> +		pcie->ops->write(addr, 0x2, value);
> +		return;
> +	}
> +
> +	writew(value, addr);
>  }

cdns_pcie_writeb and cdns_pcie_writew are used, so remove them.

>  
>  static inline void cdns_pcie_writel(struct cdns_pcie *pcie, u32 reg, u32 value)
>  {
> -	writel(value, pcie->reg_base + reg);
> +	void __iomem *addr = pcie->reg_base + reg;
> +
> +	if (pcie->ops && pcie->ops->write) {
> +		pcie->ops->write(addr, 0x4, value);
> +		return;
> +	}
> +
> +	writel(value, addr);

writel isn't broken for you, so you don't need this either.

>  }
>  
>  static inline u32 cdns_pcie_readl(struct cdns_pcie *pcie, u32 reg)
>  {
> -	return readl(pcie->reg_base + reg);
> +	void __iomem *addr = pcie->reg_base + reg;
> +
> +	if (pcie->ops && pcie->ops->read)
> +		return pcie->ops->read(addr, 0x4);
> +
> +	return readl(addr);

And neither is readl.

>  }
>  
>  /* Root Port register access */
>  static inline void cdns_pcie_rp_writeb(struct cdns_pcie *pcie,
>  				       u32 reg, u8 value)
>  {
> -	writeb(value, pcie->reg_base + CDNS_PCIE_RP_BASE + reg);
> +	void __iomem *addr = pcie->reg_base + CDNS_PCIE_RP_BASE + reg;
> +
> +	if (pcie->ops && pcie->ops->write) {
> +		pcie->ops->write(addr, 0x1, value);
> +		return;
> +	}
> +
> +	writeb(value, addr);
>  }
>  
>  static inline void cdns_pcie_rp_writew(struct cdns_pcie *pcie,
>  				       u32 reg, u16 value)
>  {
> -	writew(value, pcie->reg_base + CDNS_PCIE_RP_BASE + reg);
> +	void __iomem *addr = pcie->reg_base + CDNS_PCIE_RP_BASE + reg;
> +
> +	if (pcie->ops && pcie->ops->write) {
> +		pcie->ops->write(addr, 0x2, value);
> +		return;
> +	}
> +
> +	writew(value, addr);

You removed 2 out of 3 calls to this. I think I'd just make the root 
port writes always be 32-bit. It is all just one time init stuff 
anyways.

Either rework the calls to assemble the data into 32-bits or keep these 
functions and do the RMW here.

>  }
>  
>  /* Endpoint Function register access */
>  static inline void cdns_pcie_ep_fn_writeb(struct cdns_pcie *pcie, u8 fn,
>  					  u32 reg, u8 value)
>  {
> -	writeb(value, pcie->reg_base + CDNS_PCIE_EP_FUNC_BASE(fn) + reg);
> +	void __iomem *addr = pcie->reg_base + CDNS_PCIE_EP_FUNC_BASE(fn) + reg;
> +
> +	if (pcie->ops && pcie->ops->write) {
> +		pcie->ops->write(addr, 0x1, value);
> +		return;
> +	}
> +
> +	writeb(value, addr);

Same for these EP functions. 

Unless there are places where doing a RMW is fundamentally broken like 
in config space (not counting the one time init stuff).

Rob