linux-kernel - Re: [PATCH v2 1/9] PCI: rockchip: Remove writes to unused registers

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Message-ID: <2ebd33e2-46ef-356d-ff4c-81b74950d02f@opensource.wdc.com>
Date:   Wed, 15 Feb 2023 08:56:01 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Rick Wertenbroek <rick.wertenbroek@...il.com>,
        alberto.dassatti@...g-vd.ch
Cc:     xxm@...k-chips.com, rick.wertenbroek@...g-vd.ch,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Mikko Kovanen <mikko.kovanen@...amobile.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 1/9] PCI: rockchip: Remove writes to unused registers

On 2/14/23 23:08, Rick Wertenbroek wrote:
> Remove write accesses to registers that are marked "unused" (and
> therefore read-only) in the technical reference manual (TRM)
> (see RK3399 TRM 17.6.8.1)
> 
> Signed-off-by: Rick Wertenbroek <rick.wertenbroek@...il.com>

I checked the TRM and indeed these registers are listed as unused.
However, with this patch, nothing work for me using a Pine rockpro64
board. Keeping this patch, your series (modulo some other fixes, more
emails coming) is making things work !

So I think the bug is with the TRM, not the code. THinking logically about
htis, it makes sense: this is programming the address translation unit to
translate mmio & dma between host PCI address and local CPU space address.
If we never set the PU address, how can that unit possibly ever translate
anything ?

> ---
>  drivers/pci/controller/pcie-rockchip-ep.c | 10 ----------
>  1 file changed, 10 deletions(-)
> 
> diff --git a/drivers/pci/controller/pcie-rockchip-ep.c b/drivers/pci/controller/pcie-rockchip-ep.c
> index d1a200b93..d5c477020 100644
> --- a/drivers/pci/controller/pcie-rockchip-ep.c
> +++ b/drivers/pci/controller/pcie-rockchip-ep.c
> @@ -61,10 +61,6 @@ static void rockchip_pcie_clear_ep_ob_atu(struct rockchip_pcie *rockchip,
>  			    ROCKCHIP_PCIE_AT_OB_REGION_DESC0(region));
>  	rockchip_pcie_write(rockchip, 0,
>  			    ROCKCHIP_PCIE_AT_OB_REGION_DESC1(region));
> -	rockchip_pcie_write(rockchip, 0,
> -			    ROCKCHIP_PCIE_AT_OB_REGION_CPU_ADDR0(region));
> -	rockchip_pcie_write(rockchip, 0,
> -			    ROCKCHIP_PCIE_AT_OB_REGION_CPU_ADDR1(region));
>  }
>  
>  static void rockchip_pcie_prog_ep_ob_atu(struct rockchip_pcie *rockchip, u8 fn,
> @@ -114,12 +110,6 @@ static void rockchip_pcie_prog_ep_ob_atu(struct rockchip_pcie *rockchip, u8 fn,
>  		     PCIE_CORE_OB_REGION_ADDR0_LO_ADDR);
>  		addr1 = upper_32_bits(cpu_addr);
>  	}
> -
> -	/* CPU bus address region */
> -	rockchip_pcie_write(rockchip, addr0,
> -			    ROCKCHIP_PCIE_AT_OB_REGION_CPU_ADDR0(r));
> -	rockchip_pcie_write(rockchip, addr1,
> -			    ROCKCHIP_PCIE_AT_OB_REGION_CPU_ADDR1(r));
>  }
>  
>  static int rockchip_pcie_ep_write_header(struct pci_epc *epc, u8 fn, u8 vfn,

-- 
Damien Le Moal
Western Digital Research