Re: [PATCH] ch341: Replace memory allocations with stack storage

[Johan Hovold <johan@kernel.org>]

On Fri, Feb 21, 2020 at 07:23:41PM +0000, Michael Hanselmann wrote:
> Storing a memory pointer consumes 4 or 8 bytes, depending on the
> architecture. The replaced buffers are 2 bytes, so this change not only
> avoids the overhead of memory allocation, but it also saves a small
> amount of stack storage.
> 
> Signed-off-by: Michael Hanselmann <public@hansmi.ch>
> ---
>  drivers/usb/serial/ch341.c | 32 ++++++++------------------------
>  1 file changed, 8 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
> index c5ecdcd51ffc..6875da6e746c 100644
> --- a/drivers/usb/serial/ch341.c
> +++ b/drivers/usb/serial/ch341.c
> @@ -255,16 +255,11 @@ 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;
> +	char 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);
> +	r = ch341_control_in(dev, CH341_REQ_READ_REG, 0x0706, 0, buffer, sizeof(buffer));

These buffers cannot be stack allocated as they need to be DMA-able on
all platforms.

Johan