linux-kernel - Re: [PATCH] USB: serial: cp210x: Adding tx

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Message-ID: <5620DD5D.9080602@cogentembedded.com>
Date:	Fri, 16 Oct 2015 14:19:57 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>,
	johan@...nel.org
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: cp210x: Adding tx_empty() to avoid cp2108
 failure

Hello.

On 10/16/2015 1:07 AM, Konstantin Shkolnyy wrote:

> Occasionally, writing data and immediately closing the port makes cp2108
> stop responding. The device had to be unplugged to clear the error.
> The failure is induced by shutting down the device while its Tx queue still has
> unsent data. Reporting the correct amount of those data avoids the problem.
> Adding tx_empty() has no adverse effect on other cp210x devices.
>
> Signed-off-by: Konstantin Shkolnyy <konstantin.shkolnyy@...il.com>
> ---
>   drivers/usb/serial/cp210x.c | 30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
>
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index eac7cca..0189e64 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
[...]
> @@ -249,6 +251,16 @@ static struct usb_serial_driver * const serial_drivers[] = {
>   #define CP210X_GET_CHARS	0x0E
>   #define CP210X_GET_PROPS	0x0F
>   #define CP210X_GET_COMM_STATUS	0x10
> +/* Data returned by CP210X_GET_COMM_STATUS -- h/w doc says it's 0x13 bytes */
> +struct cp210x_comm_status {
> +	u32     errors;
> +	u32     hold_reasons;
> +	u32     amount_in_in_queue;
> +	u32     amount_in_out_queue;
> +	u8      eof_received;
> +	u8      wait_for_immediate;
> +	u8      reserved;
> +};

    Please don't declare structures amidst of the command #define's.

>   #define CP210X_RESET		0x11
>   #define CP210X_PURGE		0x12
>   #define CP210X_SET_FLOW		0x13
> @@ -479,6 +491,24 @@ static void cp210x_close(struct usb_serial_port *port)
>   	cp210x_set_config_single(port, CP210X_IFC_ENABLE, UART_DISABLE);
>   }
>
> +static bool cp210x_tx_empty(struct usb_serial_port *port)
> +{
> +	int err;
> +

    Empty line hardly needed here.

> +	/* get_config needs "array of integers large enough", so pad to 0x14 bytes */
> +	struct cp210x_comm_status_container {
> +		struct cp210x_comm_status  sts; /* 0x13 bytes */
> +		u8                         pad_to_0x14_bytes;
> +	} comm_sts_cont;
> +
> +	err = cp210x_get_config(port, CP210X_GET_COMM_STATUS, (unsigned int *) &comm_sts_cont, 0x13);
> +

    Empty line hardly needed here.

> +	if (!err)
> +		if (comm_sts_cont.sts.amount_in_out_queue)

    Why not collapse these two *if* statements into one?

> +			return false;
> +	return true;
> +}
> +
[...]

MBR, Sergei

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