From 3f7a73b57c2f57aa25342ebdb7312f78c68502eb Mon Sep 17 00:00:00 2001 From: David Brown Date: Tue, 12 Mar 2013 11:41:51 -0700 Subject: ssbi: Comment the use of udelay() The ssbi driver uses a busywait loop to read its status register. Add a comment explaining the timing of the device itself so that future developers can better understand this delay, and possibly diagnose any problems. Signed-off-by: David Brown Signed-off-by: Greg Kroah-Hartman --- drivers/ssbi/ssbi.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/ssbi/ssbi.c b/drivers/ssbi/ssbi.c index 6fbcb25907f..7ae892590c7 100644 --- a/drivers/ssbi/ssbi.c +++ b/drivers/ssbi/ssbi.c @@ -87,6 +87,15 @@ static inline void ssbi_writel(struct msm_ssbi *ssbi, u32 val, u32 reg) writel(val, ssbi->base + reg); } +/* + * Via private exchange with one of the original authors, the hardware + * should generally finish a transaction in about 5us. The worst + * case, is when using the arbiter and both other CPUs have just + * started trying to use the SSBI bus will result in a time of about + * 20us. It should never take longer than this. + * + * As such, this wait merely spins, with a udelay. + */ static int ssbi_wait_mask(struct msm_ssbi *ssbi, u32 set_mask, u32 clr_mask) { u32 timeout = SSBI_TIMEOUT_US; @@ -161,6 +170,10 @@ err: return ret; } +/* + * See ssbi_wait_mask for an explanation of the time and the + * busywait. + */ static inline int msm_ssbi_pa_transfer(struct msm_ssbi *ssbi, u32 cmd, u8 *data) { -- cgit v1.2.3