Remove busy looping during watchdog reset.
Each polling of W_PEND_WTGR bit ("finish posted
write") after watchdog reset takes 120-140us
on BeagleBone Black board. Current U-Boot code
has watchdog resets in random places and often
there is situation when watchdog is reset
few times in a row in nested functions.
This adds extra delays and slows the whole system.Instead of polling W_PEND_WTGR bit, we skip watchdog reset if the bit is set. Anyway, watchdog is in the middle of reset *right now*, so we can just return. This noticeably increases performance of the system. Below are some measurements on BBB: - DFU upload over USB 15% faster - fastboot image upload 3x times faster - USB ep0 transfers with 4k packets 20% faster Signed-off-by: Ruslan Bilovol <[email protected]> --- drivers/watchdog/omap_wdt.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/drivers/watchdog/omap_wdt.c b/drivers/watchdog/omap_wdt.c index 7b1f429..d724c96 100644 --- a/drivers/watchdog/omap_wdt.c +++ b/drivers/watchdog/omap_wdt.c @@ -53,16 +53,25 @@ void hw_watchdog_reset(void) { struct wd_timer *wdt = (struct wd_timer *)WDT_BASE; - /* wait for posted write to complete */ - while ((readl(&wdt->wdtwwps)) & WDT_WWPS_PEND_WTGR) - ; + /* + * Somebody just triggered watchdog reset and write to WTGR register + * is in progress. It is resetting right now, no need to trigger it + * again + */ + if ((readl(&wdt->wdtwwps)) & WDT_WWPS_PEND_WTGR) + return; wdt_trgr_pattern = ~wdt_trgr_pattern; writel(wdt_trgr_pattern, &wdt->wdtwtgr); - /* wait for posted write to complete */ - while ((readl(&wdt->wdtwwps) & WDT_WWPS_PEND_WTGR)) - ; + /* + * Don't wait for posted write to complete, i.e. don't check + * WDT_WWPS_PEND_WTGR bit in WWPS register. There is no writes to + * WTGR register outside of this func, and if entering it + * we see WDT_WWPS_PEND_WTGR bit set, it means watchdog reset + * was just triggered. This prevents us from wasting time in busy + * polling of WDT_WWPS_PEND_WTGR bit. + */ } static int omap_wdt_set_timeout(unsigned int timeout) -- 1.9.1 _______________________________________________ U-Boot mailing list [email protected] https://lists.denx.de/listinfo/u-boot
