Date:   Wed, 27 Oct 2021 15:04:09 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Himadri Pandya <himadrispandya@...il.com>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] USB: serial: ch314: use usb_control_msg_recv()
 and usb_control_msg_send()

On Fri, Oct 01, 2021 at 08:57:19AM +0200, Himadri Pandya wrote:
> usb_control_msg_send/recv are new wrapper functions for usb_control_msg()
> that have proper error checks for short reads. These functions can also
> accept data buffer on stack. Hence use these functions to simplify error
> handling for short reads. Short reads will now get reported as
> -EREMOTEIO with no indication of how short the transfer was.

You're no longer using usb_control_msg_send() so the commit message
including Subject needs to be updated.

> Signed-off-by: Himadri Pandya <himadrispandya@...il.com>
> ---
> Changes in v3:
>  - Rephrase the commit message
>  - Include a note on not reporting size of the short reads in the commit
>  - Drop unnecessary changes in ch341_control_out()
>  - Drop a non-relevant style change
>  - Remove some more "out" labels
>  - Remove unnecessary return statement from a void function
> 
> Changes in v2:
>  - Fix callers of ch341_control_out() and ch341_control_in()
>  - Remove label "out"
>  - Remove an unnecessary assignment statement
> ---
>  drivers/usb/serial/ch341.c | 90 ++++++++++----------------------------
>  1 file changed, 24 insertions(+), 66 deletions(-)
> 
> diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
> index 2db917eab799..8aecc1f0dee4 100644
> --- a/drivers/usb/serial/ch341.c
> +++ b/drivers/usb/serial/ch341.c
> @@ -131,23 +131,13 @@ static int ch341_control_in(struct usb_device *dev,
>  	dev_dbg(&dev->dev, "%s - (%02x,%04x,%04x,%u)\n", __func__,
>  		request, value, index, bufsize);
>  
> -	r = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), request,
> -			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
> -			    value, index, buf, bufsize, DEFAULT_TIMEOUT);
> -	if (r < (int)bufsize) {
> -		if (r >= 0) {
> -			dev_err(&dev->dev,
> -				"short control message received (%d < %u)\n",
> -				r, bufsize);
> -			r = -EIO;
> -		}
> -
> -		dev_err(&dev->dev, "failed to receive control message: %d\n",
> -			r);
> -		return r;
> -	}
> +	r = usb_control_msg_recv(dev, 0, request,
> +				 USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
> +				 value, index, buf, bufsize, DEFAULT_TIMEOUT, GFP_KERNEL);

Line is now over 80 chars for no good reason.

> +	if (r)
> +		dev_err(&dev->dev, "failed to receive control message: %d\n", r);

Here too.

>  
> -	return 0;
> +	return r;

I'd prefer returning the errno in the error path above and keep an
explicit zero here.

>  }
>  
>  #define CH341_CLKRATE		48000000
> @@ -287,23 +277,18 @@ static int ch341_set_handshake(struct usb_device *dev, u8 control)
>  static int ch341_get_status(struct usb_device *dev, struct ch341_private *priv)
>  {
>  	const unsigned int size = 2;
> -	char *buffer;
> +	u8 buffer[2];
>  	int r;
>  	unsigned long flags;
>  
> -	buffer = kmalloc(size, GFP_KERNEL);
> -	if (!buffer)
> -		return -ENOMEM;
> -
>  	r = ch341_control_in(dev, CH341_REQ_READ_REG, 0x0706, 0, buffer, size);
> -	if (r < 0)
> -		goto out;
> +	if (r)
> +		return r;
>  
>  	spin_lock_irqsave(&priv->lock, flags);
>  	priv->msr = (~(*buffer)) & CH341_BITS_MODEM_STAT;
>  	spin_unlock_irqrestore(&priv->lock, flags);
>  
> -out:	kfree(buffer);
>  	return r;

This should now be

	return 0;

>  }
>  
> @@ -312,30 +297,25 @@ out:	kfree(buffer);
>  static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
>  {
>  	const unsigned int size = 2;
> -	char *buffer;
> +	u8 buffer[2];
>  	int r;
>  
> -	buffer = kmalloc(size, GFP_KERNEL);
> -	if (!buffer)
> -		return -ENOMEM;
> -
>  	/* expect two bytes 0x27 0x00 */
>  	r = ch341_control_in(dev, CH341_REQ_READ_VERSION, 0, 0, buffer, size);
> -	if (r < 0)
> -		goto out;
> +	if (r)
> +		return r;
>  	dev_dbg(&dev->dev, "Chip version: 0x%02x\n", buffer[0]);
>  
>  	r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT, 0, 0);
> -	if (r < 0)
> -		goto out;
> +	if (r)
> +		return r;

Now an unrelated change.

>  
>  	r = ch341_set_baudrate_lcr(dev, priv, priv->baud_rate, priv->lcr);
>  	if (r < 0)
> -		goto out;
> +		return r;
>  
>  	r = ch341_set_handshake(dev, priv->mcr);
>  
> -out:	kfree(buffer);
>  	return r;

This looks a bit inconsistent now so I'll make this an explicit return
0 too.

>  }
>  
> @@ -345,39 +325,23 @@ static int ch341_detect_quirks(struct usb_serial_port *port)
>  	struct usb_device *udev = port->serial->dev;
>  	const unsigned int size = 2;
>  	unsigned long quirks = 0;
> -	char *buffer;
> +	u8 buffer[2];
>  	int r;
>  
> -	buffer = kmalloc(size, GFP_KERNEL);
> -	if (!buffer)
> -		return -ENOMEM;
> -
>  	/*
>  	 * A subset of CH34x devices does not support all features. The
>  	 * prescaler is limited and there is no support for sending a RS232
>  	 * break condition. A read failure when trying to set up the latter is
>  	 * used to detect these devices.
>  	 */
> -	r = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0), CH341_REQ_READ_REG,
> -			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
> -			    CH341_REG_BREAK, 0, buffer, size, DEFAULT_TIMEOUT);
> +	r = usb_control_msg_recv(udev, 0, CH341_REQ_READ_REG,
> +				 USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
> +				 CH341_REG_BREAK, 0, &buffer, size, DEFAULT_TIMEOUT, GFP_KERNEL);

Unnecessarily long line > 80 chars.

>  	if (r == -EPIPE) {
>  		dev_info(&port->dev, "break control not supported, using simulated break\n");
>  		quirks = CH341_QUIRK_LIMITED_PRESCALER | CH341_QUIRK_SIMULATE_BREAK;
> -		r = 0;

Oops, you just broke the driver. :(

This request is used to detect quirky devices and a return value of
-EPIPE here should not abort probe by returning an error to the caller
of this function.

> -		goto out;
> -	}
> -
> -	if (r != size) {
> -		if (r >= 0)
> -			r = -EIO;
> +	} else if (r)

And you still need brackets on the else branch.

>  		dev_err(&port->dev, "failed to read break control: %d\n", r);
> -		goto out;
> -	}
> -
> -	r = 0;
> -out:
> -	kfree(buffer);
>  
>  	if (quirks) {
>  		dev_dbg(&port->dev, "enabling quirk flags: 0x%02lx\n", quirks);
> @@ -647,23 +611,19 @@ static void ch341_break_ctl(struct tty_struct *tty, int break_state)
>  	struct ch341_private *priv = usb_get_serial_port_data(port);
>  	int r;
>  	uint16_t reg_contents;
> -	uint8_t *break_reg;
> +	uint8_t break_reg[2];
>  
>  	if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK) {
>  		ch341_simulate_break(tty, break_state);
>  		return;
>  	}
>  
> -	break_reg = kmalloc(2, GFP_KERNEL);
> -	if (!break_reg)
> -		return;
> -
>  	r = ch341_control_in(port->serial->dev, CH341_REQ_READ_REG,
>  			ch341_break_reg, 0, break_reg, 2);
> -	if (r < 0) {
> +	if (r) {
>  		dev_err(&port->dev, "%s - USB control read error (%d)\n",
>  				__func__, r);
> -		goto out;
> +		return;
>  	}
>  	dev_dbg(&port->dev, "%s - initial ch341 break register contents - reg1: %x, reg2: %x\n",
>  		__func__, break_reg[0], break_reg[1]);
> @@ -681,11 +641,9 @@ static void ch341_break_ctl(struct tty_struct *tty, int break_state)
>  	reg_contents = get_unaligned_le16(break_reg);
>  	r = ch341_control_out(port->serial->dev, CH341_REQ_WRITE_REG,
>  			ch341_break_reg, reg_contents);
> -	if (r < 0)
> +	if (r)

Now also an unrelated change.

>  		dev_err(&port->dev, "%s - USB control write error (%d)\n",
>  				__func__, r);
> -out:
> -	kfree(break_reg);
>  }
>  
>  static int ch341_tiocmset(struct tty_struct *tty,

I've fixed up the above so we don't have to spend any more time on this.

The result is here

	https://git.kernel.org/pub/scm/linux/kernel/git/johan/usb-serial.git/commit/?h=usb-next&id=74f266455062c158f343bc3aa35ef84b3eb7adf1

Johan

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