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Date:   Mon, 26 Aug 2019 11:55:42 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>
cc:     gregkh@linuxfoundation.org, <linux-usb@vger.kernel.org>,
        <usb-storage@lists.one-eyed-alien.net>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] USB: storage: ums-realtek: Make auto-delink
 support optionally
In-Reply-To: <20190826054216.31468-2-kai.heng.feng@canonical.com>
Message-ID: <Pine.LNX.4.44L0.1908261141110.1662-100000@iolanthe.rowland.org>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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On Mon, 26 Aug 2019, Kai-Heng Feng wrote:

> Auto-delink requires writing special registers to ums-realtek device.
> Unconditionally enable auto-delink may break newer devices.
> 
> So only enable auto-delink by default for the original three IDs,
> 0x0138, 0x0158 and 0x0159.
> 
> Realtek is working on a patch to properly support auto-delink for other
> IDs.
> 
> BugLink: https://bugs.launchpad.net/bugs/1838886
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
> v2:
> - Use auto_delink_support instead of auto_delink_enable.
> 
> drivers/usb/storage/realtek_cr.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/storage/realtek_cr.c b/drivers/usb/storage/realtek_cr.c
> index beaffac805af..b304cca7c4fa 100644
> --- a/drivers/usb/storage/realtek_cr.c
> +++ b/drivers/usb/storage/realtek_cr.c
> @@ -40,6 +40,10 @@ static int auto_delink_en = 1;
>  module_param(auto_delink_en, int, S_IRUGO | S_IWUSR);
>  MODULE_PARM_DESC(auto_delink_en, "auto delink mode (0=firmware, 1=software [default])");
>  
> +static int auto_delink_support = -1;
> +module_param(auto_delink_support, int, S_IRUGO | S_IWUSR);
> +MODULE_PARM_DESC(auto_delink_support, "enable auto delink (-1=auto [default], 0=disable, 1=enable)");
> +
>  #ifdef CONFIG_REALTEK_AUTOPM
>  static int ss_en = 1;
>  module_param(ss_en, int, S_IRUGO | S_IWUSR);
> @@ -996,12 +1000,22 @@ static int init_realtek_cr(struct us_data *us)
>  			goto INIT_FAIL;
>  	}
>  
> -	if (CHECK_FW_VER(chip, 0x5888) || CHECK_FW_VER(chip, 0x5889) ||
> -	    CHECK_FW_VER(chip, 0x5901))
> -		SET_AUTO_DELINK(chip);
> -	if (STATUS_LEN(chip) == 16) {
> -		if (SUPPORT_AUTO_DELINK(chip))
> +	if (auto_delink_support == -1) {
> +		if (CHECK_PID(chip, 0x0138) || CHECK_PID(chip, 0x0158) ||
> +		    CHECK_PID(chip, 0x0159))
> +			auto_delink_support = 1;
> +		else
> +			auto_delink_support = 0;
> +	}

What will happen if somebody has two Realtek devices plugged in, where
one of them has an old product ID and the other has a new one?  You
shouldn't change the value of the module parameter like this.

> +
> +	if (auto_delink_support) {
> +		if (CHECK_FW_VER(chip, 0x5888) || CHECK_FW_VER(chip, 0x5889) ||
> +				CHECK_FW_VER(chip, 0x5901))
>  			SET_AUTO_DELINK(chip);
> +		if (STATUS_LEN(chip) == 16) {
> +			if (SUPPORT_AUTO_DELINK(chip))
> +				SET_AUTO_DELINK(chip);
> +		}
>  	}
>  #ifdef CONFIG_REALTEK_AUTOPM
>  	if (ss_en)

Instead of adding a new module parameter, how about just changing the 
driver's behavior?  If a chip doesn't have the right product ID, don't 
enable auto_delink regardless of what the module parameter is set to.

Alan Stern