linux-kernel - Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled

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Date:   Mon, 17 May 2021 11:32:01 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Connor Davis <connojdavis@...il.com>
Cc:     Jann Horn <jannh@...gle.com>, Lee Jones <lee.jones@...aro.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled

On 14.05.2021 02:56, Connor Davis wrote:
> Check if the debug capability is enabled in early_xdbc_parse_parameter,
> and if it is, return with an error. This avoids collisions with whatever
> enabled the DbC prior to linux starting.

Doesn't this go too far and prevent use even if firmware (perhaps
mistakenly) left it enabled?

Jan

> Signed-off-by: Connor Davis <connojdavis@...il.com>
> ---
>  drivers/usb/early/xhci-dbc.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
> index be4ecbabdd58..ca67fddc2d36 100644
> --- a/drivers/usb/early/xhci-dbc.c
> +++ b/drivers/usb/early/xhci-dbc.c
> @@ -642,6 +642,16 @@ int __init early_xdbc_parse_parameter(char *s)
>  	}
>  	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
>  
> +	if (readl(&xdbc.xdbc_reg->control) & CTRL_DBC_ENABLE) {
> +		pr_notice("xhci debug capability already in use\n");
> +		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> +		xdbc.xdbc_reg = NULL;
> +		xdbc.xhci_base = NULL;
> +		xdbc.xhci_length = 0;
> +
> +		return -ENODEV;
> +	}
> +
>  	return 0;
>  }
>  
>