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@xxxxxxxxx>
> ---
> 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
