evie/android_kernel_oneplus_msm8998
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ssbi: Comment the use of udelay()

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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>
This commit is contained in:
David Brown 2013-03-12 11:41:51 -07:00 • committed by Greg Kroah-Hartman
parent 97f00f7120
commit 3f7a73b57c
1 changed files with 13 additions and 0 deletions
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13
drivers/ssbi/ssbi.c
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@ -87,6 +87,15 @@ static inline void ssbi_writel(struct msm_ssbi *ssbi, u32 val, u32 reg)
writel(val, ssbi->base + 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) static int ssbi_wait_mask(struct msm_ssbi *ssbi, u32 set_mask, u32 clr_mask)
{ {
u32 timeout = SSBI_TIMEOUT_US; u32 timeout = SSBI_TIMEOUT_US;
@ -161,6 +170,10 @@ err:
return ret; return ret;
} }
/*
* See ssbi_wait_mask for an explanation of the time and the
* busywait.
*/
static inline int static inline int
msm_ssbi_pa_transfer(struct msm_ssbi *ssbi, u32 cmd, u8 *data) msm_ssbi_pa_transfer(struct msm_ssbi *ssbi, u32 cmd, u8 *data)
{ {