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    SubjectRe: Locking in the clk API
    On 01/27/2011 12:54 AM, Russell King - ARM Linux wrote:
    > On Wed, Jan 26, 2011 at 08:34:20PM -0800, Saravana Kannan wrote:
    >> I'm not too familiar with serial/tty, does anyone know if the
    >> .set_termios needs to be atmoic? If not, we could just change
    >> cpm_uart/cpm_uart_core.c to use mutex instead of spinlock.
    >
    > The locking is there to protect against the interrupt handler accessing
    > the port->* stuff (which seems to have been forgotten by the cpm driver).
    >
    > I don't see any reason why clk_set_rate() needs to be under the spinlock
    > there - we need the reprogramming of the baud rate within the spinlock
    > on 8250 because of DLAB bit hiding the data registers. It's also a good
    > idea that it _is_ within the spinlock along with uart_update_timeout()
    > to ensure timeouts and the baud rate are updated together.

    For internal tree purposes, does .set_termios need to be atomic? Can it
    grab mutexes instead of spinlock?

    Going back to the topic, how about CPU freq drivers possibly using
    clk_set_rate() to change freq? Do you think that's not the case or a
    concern?

    All,

    Do any one of your mach's control CPU freq using clk_set_rate() and does
    it need to be atomic? CPUfreq doesn't need it to be atomic. So, you will
    need clk_set_rate() to be atomic only if you try to use it to lower CPU
    freq very late during idle/suspend.

    -Saravana

    --
    Sent by an employee of the Qualcomm Innovation Center, Inc.
    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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