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From: Alan Stern <stern@rowland.harvard.edu>
To: neal_liu <neal_liu@aspeedtech.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Tony Prisk <linux@prisktech.co.nz>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Tao Ren <rentao.bupt@gmail.com>,
	BMC-SW@aspeedtech.com
Subject: Re: [PATCH] usb: host: ehci: skip STS_HALT check for aspeed platform
Date: Thu, 26 Aug 2021 11:28:24 -0400	[thread overview]
Message-ID: <20210826152824.GC228824@rowland.harvard.edu> (raw)
In-Reply-To: <20210826071525.27651-1-neal_liu@aspeedtech.com>

On Thu, Aug 26, 2021 at 03:15:25PM +0800, neal_liu wrote:
> STS_HALT also depends on ASS/PSS status for apseed.
> Skip this check on startup.
> 
> Signed-off-by: neal_liu <neal_liu@aspeedtech.com>
> ---
>  drivers/usb/host/ehci-hcd.c      | 10 +++++++++-
>  drivers/usb/host/ehci-platform.c |  6 ++++++
>  drivers/usb/host/ehci.h          |  1 +
>  3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
> index 10b0365f3439..a539e11502ef 100644
> --- a/drivers/usb/host/ehci-hcd.c
> +++ b/drivers/usb/host/ehci-hcd.c
> @@ -634,7 +634,15 @@ static int ehci_run (struct usb_hcd *hcd)
>  	/* Wait until HC become operational */
>  	ehci_readl(ehci, &ehci->regs->command);	/* unblock posted writes */
>  	msleep(5);
> -	rc = ehci_handshake(ehci, &ehci->regs->status, STS_HALT, 0, 100 * 1000);
> +
> +	/* For Aspeed, STS_HALT also depends on ASS/PSS status.
> +	 * Skip this check on startup.
> +	 */
> +	if (ehci->is_aspeed)
> +		rc = 0;
> +	else
> +		rc = ehci_handshake(ehci, &ehci->regs->status, STS_HALT,
> +				    0, 100 * 1000);

You must not do this.  You are assuming the controller will always begin 
operating within 5 ms of the time it is told to start.  What happens if you are 
wrong?

There must be some way for the aspeed controller's host computer to tell when 
the controller has started running.  Find out what it is and use it.

Alan Stern

WARNING: multiple messages have this Message-ID (diff)
From: Alan Stern <stern@rowland.harvard.edu>
To: neal_liu <neal_liu@aspeedtech.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Tony Prisk <linux@prisktech.co.nz>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Tao Ren <rentao.bupt@gmail.com>,
	BMC-SW@aspeedtech.com
Subject: Re: [PATCH] usb: host: ehci: skip STS_HALT check for aspeed platform
Date: Thu, 26 Aug 2021 11:28:24 -0400	[thread overview]
Message-ID: <20210826152824.GC228824@rowland.harvard.edu> (raw)
In-Reply-To: <20210826071525.27651-1-neal_liu@aspeedtech.com>

On Thu, Aug 26, 2021 at 03:15:25PM +0800, neal_liu wrote:
> STS_HALT also depends on ASS/PSS status for apseed.
> Skip this check on startup.
> 
> Signed-off-by: neal_liu <neal_liu@aspeedtech.com>
> ---
>  drivers/usb/host/ehci-hcd.c      | 10 +++++++++-
>  drivers/usb/host/ehci-platform.c |  6 ++++++
>  drivers/usb/host/ehci.h          |  1 +
>  3 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
> index 10b0365f3439..a539e11502ef 100644
> --- a/drivers/usb/host/ehci-hcd.c
> +++ b/drivers/usb/host/ehci-hcd.c
> @@ -634,7 +634,15 @@ static int ehci_run (struct usb_hcd *hcd)
>  	/* Wait until HC become operational */
>  	ehci_readl(ehci, &ehci->regs->command);	/* unblock posted writes */
>  	msleep(5);
> -	rc = ehci_handshake(ehci, &ehci->regs->status, STS_HALT, 0, 100 * 1000);
> +
> +	/* For Aspeed, STS_HALT also depends on ASS/PSS status.
> +	 * Skip this check on startup.
> +	 */
> +	if (ehci->is_aspeed)
> +		rc = 0;
> +	else
> +		rc = ehci_handshake(ehci, &ehci->regs->status, STS_HALT,
> +				    0, 100 * 1000);

You must not do this.  You are assuming the controller will always begin 
operating within 5 ms of the time it is told to start.  What happens if you are 
wrong?

There must be some way for the aspeed controller's host computer to tell when 
the controller has started running.  Find out what it is and use it.

Alan Stern

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linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2021-08-26 15:28 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-26  7:15 [PATCH] usb: host: ehci: skip STS_HALT check for aspeed platform neal_liu
2021-08-26  7:15 ` neal_liu
2021-08-26 11:27 ` Greg Kroah-Hartman
2021-08-26 11:27   ` Greg Kroah-Hartman
2021-08-26 15:28 ` Alan Stern [this message]
2021-08-26 15:28   ` Alan Stern
2021-09-01  2:34   ` Neal Liu
2021-09-01  2:34     ` Neal Liu

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