linux-kernel - Re: [PATCH] PCI: mediatek: Delay 100ms to wait power and clock to become stable

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Message-ID: <20211207015323.GA26237@bhelgaas>
Date:   Mon, 6 Dec 2021 19:53:23 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     qizhong cheng <qizhong.cheng@...iatek.com>
Cc:     Ryder Lee <ryder.lee@...iatek.com>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyiński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Chuanjia Liu <chuanjia.liu@...iatek.com>,
        Jiey Yang <ot_jiey.yang@...iatek.com>
Subject: Re: [PATCH] PCI: mediatek: Delay 100ms to wait power and clock to
 become stable

On Thu, Nov 04, 2021 at 02:21:44PM +0800, qizhong cheng wrote:
> Described in PCIe CEM specification setctions 2.2 (PERST# Signal) and
> 2.2.1 (Initial Power-Up (G3 to S0)). The deassertion of PERST# should
> be delayed 100ms (TPVPERL) for the power and clock to become stable.

Thanks for the spec references.

s/setctions/sections/

> Signed-off-by: qizhong cheng <qizhong.cheng@...iatek.com>
> ---
>  drivers/pci/controller/pcie-mediatek.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
> index 2f3f974977a3..b32acbac8084 100644
> --- a/drivers/pci/controller/pcie-mediatek.c
> +++ b/drivers/pci/controller/pcie-mediatek.c
> @@ -702,6 +702,14 @@ static int mtk_pcie_startup_port_v2(struct mtk_pcie_port *port)
>  	 */
>  	writel(PCIE_LINKDOWN_RST_EN, port->base + PCIE_RST_CTRL);
>  
> +	/*
> +	 * Described in PCIe CEM specification setctions 2.2 (PERST# Signal)
> +	 * and 2.2.1 (Initial Power-Up (G3 to S0)).
> +	 * The deassertion of PERST# should be delayed 100ms (TPVPERL)
> +	 * for the power and clock to become stable.

s/setctions/sections/ again.  Otherwise we'll have a typo-fixing patch
eventually.

Please also rewrap into one paragraph.

> +	 */
> +	msleep(100);
> +
>  	/* De-assert PHY, PE, PIPE, MAC and configuration reset	*/
>  	val = readl(port->base + PCIE_RST_CTRL);
>  	val |= PCIE_PHY_RSTB | PCIE_PERSTB | PCIE_PIPE_SRSTB |
> -- 
> 2.25.1
>