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Re: [PATCH] ath9k_hw: avoid possible infinite loop in ar9003_get_pll_sqsum_dvc

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Hi Raj,

On Monday 18 June 2012 01:34 PM, Rajkumar Manoharan wrote:
On Mon, Jun 18, 2012 at 01:13:30PM +0530, Mohammed Shafi Shajakhan wrote:
From: Mohammed Shafi Shajakhan<mohammed@xxxxxxxxxxxxxxxx>

"ath9k: Fix softlockup in AR9485" with commit id
64bc1239c790e051ff677e023435d770d2ffa174 fixed the reported
issue, yet its better to avoid the possible infinite loop
in ar9003_get_pll_sqsum_dvc by having a timeout as suggested
by ath9k maintainers.
http://www.spinics.net/lists/linux-wireless/msg92126.html.
Based on my testing PLL's locking measurement is done in
~200us (2 iterations).

Cc: stable@xxxxxxxxxxxxxxx
Cc: Rolf Offermanns<rolf.offermanns@xxxxxxx>
Cc: Sujith Manoharan<c_manoha@xxxxxxxxxxxxxxxx>
Cc: Senthil Balasubramanian<senthilb@xxxxxxxxxxxxxxxx>
Signed-off-by: Mohammed Shafi Shajakhan<mohammed@xxxxxxxxxxxxxxxx>
---
  drivers/net/wireless/ath/ath9k/hw.c |   14 +++++++++++++-
  1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/hw.c b/drivers/net/wireless/ath/ath9k/hw.c
index 784baee..a42c26f 100644
--- a/drivers/net/wireless/ath/ath9k/hw.c
+++ b/drivers/net/wireless/ath/ath9k/hw.c
@@ -773,13 +773,25 @@ static void ath9k_hw_init_qos(struct ath_hw *ah)

  u32 ar9003_get_pll_sqsum_dvc(struct ath_hw *ah)
  {
+	struct ath_common *common = ath9k_hw_common(ah);
+	int i = 0;
+
  	REG_CLR_BIT(ah, PLL3, PLL3_DO_MEAS_MASK);
  	udelay(100);
  	REG_SET_BIT(ah, PLL3, PLL3_DO_MEAS_MASK);

-	while ((REG_READ(ah, PLL4)&  PLL4_MEAS_DONE) == 0)
+	while ((REG_READ(ah, PLL4)&  PLL4_MEAS_DONE) == 0) {
+
  		udelay(100);

+		if (WARN_ON_ONCE(i>= 100)) {
+			ath_err(common, "PLL4 meaurement not done\n");
+			break;
+		}
+
+		i++;
How did you come up with 100 as max limit to break the loop?


i assumed its a sufficient arbitrary max value to confirm that the PLL locking measurement does not happens. Based on my quite a few of tests(idle associated, with traffic)PLL immediately locksup in 200us (2 iterations). As per your suggestion i will quickly check with the System's team if we can give a proper value, rather than 100 * 100 us as timeout. thanks for reviewing it!

--
thanks,
shafi
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