linux-kernel - Re: [PATCH v7 2/5] PCI: dwc: add support to handle ZRX-DC Compliant PHYs

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Date:   Thu, 7 Jan 2021 12:44:06 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Shradha Todi <shradha.t@...sung.com>
Cc:     linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pci@...r.kernel.org, pankaj.dubey@...sung.com,
        sriram.dash@...sung.com, niyas.ahmed@...sung.com,
        p.rajanbabu@...sung.com, l.mehra@...sung.com, hari.tv@...sung.com,
        Anvesh Salveru <anvesh.salveru@...il.com>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v7 2/5] PCI: dwc: add support to handle ZRX-DC Compliant
 PHYs

Capitalize subject to match the rest of the series.

"Add support to handle .." is redundant; "Add support for ..." would
be equivalent and shorter.

But this patch actually doesn't add anything at all by itself, since
it checks pci->phy_zrxdc_compliant but never sets it.

On Thu, Jan 07, 2021 at 08:58:40PM +0530, Shradha Todi wrote:
> From: Pankaj Dubey <pankaj.dubey@...sung.com>
> 
> Many platforms use DesignWare controller but the PHY can be different in
> different platforms. If the PHY is compliant is to ZRX-DC specification it
> helps in low power consumption during power states.

s/is to/to/

Even with that, this sentence doesn't quite parse correctly.  Do you
mean something like this?

  If the PHY is compliant to the ZRX-DC specification, it reduces
  power consumption in low power Link states.

(I assume this is related to Link power states (L0, L1, etc), not
device power states (D0, D3hot, etc)).

> If current data rate is 8.0 GT/s or higher and PHY is not compliant to
> ZRX-DC specification, then after every 100ms link should transition to
> recovery state during the low power states.

Not sure this makes sense.  If the Link is in a low power state for 10
seconds, it must transition to the Recovery state every 100ms during
that 10 seconds, i.e., 100 times?

> DesignWare controller provides GEN3_ZRXDC_NONCOMPL field in
> GEN3_RELATED_OFF to specify about ZRX-DC compliant PHY.
> 
> Platforms with ZRX-DC compliant PHY can set phy_zrxdc_compliant variable to
> specify this property to the controller.

If this is a DesignWare-generic register and the "phy-zrxdc-compliant"
property can be used by any DesignWare-based driver, why isn't the
code to look for it in the DesignWare-generic part?

Is there a link to the ZRX-DC specification you can mention somewhere
in this series?

> Signed-off-by: Anvesh Salveru <anvesh.salveru@...il.com>
> Signed-off-by: Pankaj Dubey <pankaj.dubey@...sung.com>
> Signed-off-by: Shradha Todi <shradha.t@...sung.com>
> Cc: Jingoo Han <jingoohan1@...il.com>
> Cc: Gustavo Pimentel <gustavo.pimentel@...opsys.com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Rob Herring <robh@...nel.org>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 6 ++++++
>  drivers/pci/controller/dwc/pcie-designware.h | 4 ++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 645fa18..74590c7 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -722,4 +722,10 @@ void dw_pcie_setup(struct dw_pcie *pci)
>  		       PCIE_PL_CHK_REG_CHK_REG_START;
>  		dw_pcie_writel_dbi(pci, PCIE_PL_CHK_REG_CONTROL_STATUS, val);
>  	}
> +
> +	if (pci->phy_zrxdc_compliant) {
> +		val = dw_pcie_readl_dbi(pci, PCIE_PORT_GEN3_RELATED);
> +		val &= ~PORT_LOGIC_GEN3_ZRXDC_NONCOMPL;
> +		dw_pcie_writel_dbi(pci, PCIE_PORT_GEN3_RELATED, val);
> +	}
>  }
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 0207840..8b905a2 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -74,6 +74,9 @@
>  #define PCIE_MSI_INTR0_MASK		0x82C
>  #define PCIE_MSI_INTR0_STATUS		0x830
>  
> +#define PCIE_PORT_GEN3_RELATED		0x890
> +#define PORT_LOGIC_GEN3_ZRXDC_NONCOMPL	BIT(0)
> +
>  #define PCIE_PORT_MULTI_LANE_CTRL	0x8C0
>  #define PORT_MLTI_UPCFG_SUPPORT		BIT(7)
>  
> @@ -273,6 +276,7 @@ struct dw_pcie {
>  	u8			n_fts[2];
>  	bool			iatu_unroll_enabled: 1;
>  	bool			io_cfg_atu_shared: 1;
> +	bool			phy_zrxdc_compliant;

I raise my eyebrows a little at "bool xx : 1".  I think it's probably
*correct*, but "unsigned int xx : 1" is the overwhelming favorite and
I doubt bool gives any advantage.

  $ git grep -E "int\s+\S+\s*:\s*1" | egrep "^\S*\.[ch]" | wc -l
  3129
  $ git grep -E "bool\s+\S+\s*:\s*1" | egrep "^\S*\.[ch]" | wc -l
  637

pcie-designware.h is the only user in drivers/pci.  But you're
following the existing style in the file, which is good.

>  };
>  
>  #define to_dw_pcie_from_pp(port) container_of((port), struct dw_pcie, pp)
> -- 
> 2.7.4
>