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| author | David Brown <davidb@codeaurora.org> | 2013-03-12 19:41:51 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-03-25 18:39:40 +0100 |
| commit | 3f7a73b57c2f57aa25342ebdb7312f78c68502eb (patch) | |
| tree | 068b9fcf5ffe224ab011c633cf83219282497c72 | |
| parent | SSBI: Convert SSBI to device tree (diff) | |
| download | linux-3f7a73b57c2f57aa25342ebdb7312f78c68502eb.tar.xz linux-3f7a73b57c2f57aa25342ebdb7312f78c68502eb.zip | |
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 <davidb@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/ssbi/ssbi.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/ssbi/ssbi.c b/drivers/ssbi/ssbi.c index 6fbcb25907ff..7ae892590c75 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) { |