Re: [PATCH 3/4] pch_uart: Add user_uartclk parameter

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Feb 29, 2012 at 10:24:46AM -0800, Darren Hart wrote:
> For cases where boards with non-default clocks are not yet added to the kernel
> or when the clock varies across hardware revisions, it is useful to be
> able to specify the UART clock on the kernel command line.
> 
> Add the user_uartclk parameter and prefer it, if set, to the default and
> board specific UART clock settings. Specify user_uartclock on the command-line
> with "pch_uart.user_uartclk=48000000".
> 
> Signed-off-by: Darren Hart <dvhart@linux.intel.com>
> CC: Tomoya MORINAGA <tomoya.rohm@gmail.com>
> CC: Feng Tang <feng.tang@intel.com>
> CC: Alan Cox <alan@linux.intel.com>
> ---
>  drivers/tty/serial/pch_uart.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
> index 3a2b0ae..105d982 100644
> --- a/drivers/tty/serial/pch_uart.c
> +++ b/drivers/tty/serial/pch_uart.c
> @@ -290,6 +290,7 @@ static struct pch_uart_driver_data drv_dat[] = {
>  static struct eg20t_port *pch_uart_ports[PCH_UART_NR];
>  #endif
>  static unsigned int default_baud = 9600;
> +static unsigned int user_uartclk = 0;
>  static const int trigger_level_256[4] = { 1, 64, 128, 224 };
>  static const int trigger_level_64[4] = { 1, 16, 32, 56 };
>  static const int trigger_level_16[4] = { 1, 4, 8, 14 };
> @@ -300,6 +301,9 @@ static int pch_uart_get_uartclk(void)
>  {
>  	const char *cmp;
>  
> +	if (user_uartclk)
> +		return user_uartclk;
> +
>  	cmp = dmi_get_system_info(DMI_BOARD_NAME);
>  	if (cmp && strstr(cmp, "CM-iTC"))
>  		return CMITC_UARTCLK;
> @@ -1799,3 +1803,4 @@ module_exit(pch_uart_module_exit);
>  MODULE_LICENSE("GPL v2");
>  MODULE_DESCRIPTION("Intel EG20T PCH UART PCI Driver");
>  module_param(default_baud, uint, S_IRUGO);
> +module_param(user_uartclk, uint, S_IRUGO);

I don't object to this, but you should provide some documentation on
what this option does.  How about a follow-on patch using
MODULE_PARM_DESC() for both of these options to help people out with how
they should be used?

thanks,

greg k-h