linux-kernel - RE: Patch "USB: serial: mos7840: Supported MCS7810 device"

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Message-ID: <002e01cd0e1b$2d01f020$8705d060$@com.tw>
Date:	Fri, 30 Mar 2012 10:16:48 +0800
From:	"Donald" <donald@...x.com.tw>
To:	"'Alan Cox'" <alan@...rguk.ukuu.org.uk>
Cc:	"'Greg KH'" <gregkh@...uxfoundation.org>,
	"'open list:USB SUBSYSTEM'" <linux-usb@...r.kernel.org>,
	"'open list'" <linux-kernel@...r.kernel.org>
Subject: RE: Patch "USB: serial: mos7840: Supported MCS7810 device"

Hi Alan,

Thank you for your kind comments for this patch. I will refine the patch
according to your comments and re-submit it then.

Regards,
Donald

-----Original Message-----
From: Alan Cox [mailto:alan@...rguk.ukuu.org.uk] 
Sent: Thursday, March 29, 2012 11:04 PM
To: Donald
Cc: 'Greg KH'; 'open list:USB SUBSYSTEM'; 'open list'
Subject: Re: Patch "USB: serial: mos7840: Supported MCS7810 device"


> +static void mos7810_control_callback(struct urb *urb) {
> +	if (!urb)
> +		return;

How can this ever occur. If its not theoretically possible then this check
is just going to hide bugs in future.

> +static void mos7810_led_off(unsigned long arg) {
> +	struct moschip_port *mcs = (struct moschip_port *) arg;
> +
> +	if (!mcs)
> +		return;

Ditto

> +	/* Turn on MCS7810 LED */
> +	if (serial->num_ports == 1 && mos7840_port->mos7810_led_flag == 0) {
> +		mos7840_port->mos7810_led_flag = 1;
> +		mos7810_set_reg(mos7840_port, 0x0301,
> MODEM_CONTROL_REGISTER);
> +		mod_timer(&mos7840_port->mos7810_led_timer1, jiffies + 500);
> +	}

The assumption that serial->num_ports = 1 means "has LED" is going to cause
problems later if another deivce appears with 1 port and no LED. I think it
would be much clearer to have something like

	if (mos7840_port->has_led)

for these tests of the driver

> +static int mos7810_check(struct usb_serial *serial) {
> +	int i, pass_count = 0;
> +	__u16 Data = 0, MCR_Data = 0;
> +	__u16 test_pattern = 0x55AA, write_pattern;

generally linux style is all lower case for egister names. Not a big deal

> +		/* If this a MCS7810 device, both test patterns must match
> */
> +		if (((test_pattern >> i) & 0x0001) != ((~(Data >> 1)) &
> 0x0001))

		if (((test_pattern >> i) ^ (~Data >> 1)) & 0x0001) ?

again trivia...


> +			mos7840_port->mos7810_led_timer1.expires =
> +							jiffies + 500;

This 500 value depends upon the HZ value of the kernel which won't always be
1000 on all platforms. You probably want

			jiffies + msecs_to_jiffies(500);

(or indeed HZ/2)

> +				/* Turn off MCS7810 LED */
> +				usb_control_msg(serial->dev,
> +					usb_sndctrlpipe(serial->dev, 0),
> +					MCS_WRREQ, MCS_WR_RTYPE, 0x0300,
> +					MODEM_CONTROL_REGISTER,	NULL, 0,
> +					MOS_WDR_TIMEOUT);
> +

Might be clearer if these occurences were a separate small function - gcc
will inline them if it makes sense, and it will be clearer.


Alan


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