linux-kernel - Re: [PATCH v2 2/3] PCI: qcom: Read back PARF

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Date: Mon, 12 Feb 2024 15:17:03 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH v2 2/3] PCI: qcom: Read back PARF_LTSSM register

Maybe include the reason in the subject?  "Read back" is literally
what the diff says.

On Sat, Feb 10, 2024 at 06:10:06PM +0100, Konrad Dybcio wrote:
> To ensure write completion, read the PARF_LTSSM register after setting
> the LTSSM enable bit before polling for "link up".

The write will obviously complete *some* time; I assume the point is
that it's important for it to complete before some other event, and it
would be nice to know why that's important.

> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index cbde9effa352..6a469ed213ce 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -539,6 +539,7 @@ static void qcom_pcie_2_3_2_ltssm_enable(struct qcom_pcie *pcie)
>  	val = readl(pcie->parf + PARF_LTSSM);
>  	val |= LTSSM_EN;
>  	writel(val, pcie->parf + PARF_LTSSM);
> +	readl(pcie->parf + PARF_LTSSM);
>  }
>  
>  static int qcom_pcie_get_resources_2_3_2(struct qcom_pcie *pcie)
> 
> -- 
> 2.40.1
>