linux-kernel - Re: [PATCH] PCI: mediatek: Verify whether the free

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Message-ID: <20210429223838.GA588275@bjorn-Precision-5520>
Date:   Thu, 29 Apr 2021 17:38:38 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Amey Narkhede <ameynarkhede03@...il.com>
Cc:     Ryder Lee <ryder.lee@...iatek.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] PCI: mediatek: Verify whether the free_ck clock is
 ungated or not

Can you make the subject say something at a higher level instead of
just paraphrasing the C code?  I'm guessing this means resume will now
fail if the clock isn't turned on?

On Thu, Apr 29, 2021 at 07:17:49PM +0530, Amey Narkhede wrote:
> Verify that the free_ck clock is ungated on device resume
> by checking return value of clk_prepare_enable().

Also the commit log -- this doesn't say anything more than the code
itself.  Did you find this by tripping over it?  Or just by code
inspection?  I guess without the check, we continue on and try to
resume, but accesses to PCI devices fail and maybe return ~0 data or
cause machine checks or something?

> Signed-off-by: Amey Narkhede <ameynarkhede03@...il.com>
> ---
>  drivers/pci/controller/pcie-mediatek.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-mediatek.c b/drivers/pci/controller/pcie-mediatek.c
> index 23548b517..9b13214bf 100644
> --- a/drivers/pci/controller/pcie-mediatek.c
> +++ b/drivers/pci/controller/pcie-mediatek.c
> @@ -1154,11 +1154,14 @@ static int __maybe_unused mtk_pcie_resume_noirq(struct device *dev)
>  {
>  	struct mtk_pcie *pcie = dev_get_drvdata(dev);
>  	struct mtk_pcie_port *port, *tmp;
> +	int ret;
> 
>  	if (list_empty(&pcie->ports))
>  		return 0;
> 
> -	clk_prepare_enable(pcie->free_ck);
> +	ret = clk_prepare_enable(pcie->free_ck);
> +	if (ret)
> +		return ret;

Most callers print an error message when clk_prepare_enable() fails.

>  	list_for_each_entry_safe(port, tmp, &pcie->ports, list)
>  		mtk_pcie_enable_port(port);
> --
> 2.31.1