I tried the following mainline kernel versions a few days and there was no "ath5k phy0: gain calibration timeout" message.:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3.3-precise/
http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3.4-precise/

In mainline kernel http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3.5-precise/ I get the "ath5k phy0: gain calibration timeout" message and I lost the wifi-connection.

~$ dmesg | grep ath
[   14.034277] ath5k 0000:14:00.0: registered as 'phy0'
[   14.565049] ath: EEPROM regdomain: 0x65
[   14.565053] ath: EEPROM indicates we should expect a direct regpair map
[   14.565058] ath: Country alpha2 being used: 00
[   14.565060] ath: Regpair used: 0x65
[   14.903629] ath5k phy0: Atheros AR2425 chip found (MAC: 0xe2, PHY: 0x70)
[15003.008997] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[15363.006203] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[32763.008753] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[40083.002586] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[42963.003379] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[52923.006883] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[54123.006255] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[54603.008746] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[55203.007999] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[57183.008557] ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[60486.862594] ath5k phy0: gain calibration timeout (2412MHz)
[60487.192863] ath5k phy0: calibration of channel 1 failed
[60489.966013] ath5k phy0: gain calibration timeout (2412MHz)
[60490.561516] ath5k phy0: gain calibration timeout (2417MHz)
[60491.157448] ath5k phy0: gain calibration timeout (2422MHz)
[60491.646579] ath5k phy0: gain calibration timeout (2427MHz)
[60492.132769] ath5k phy0: gain calibration timeout (2432MHz)
[60492.619133] ath5k phy0: gain calibration timeout (2437MHz)
[60493.103376] ath5k phy0: gain calibration timeout (2442MHz)
[60493.587244] ath5k phy0: gain calibration timeout (2447MHz)
[60494.071599] ath5k phy0: gain calibration timeout (2452MHz)
[60494.555405] ath5k phy0: gain calibration timeout (2457MHz)
[60495.042887] ath5k phy0: gain calibration timeout (2462MHz)
[60495.526887] ath5k phy0: gain calibration timeout (2467MHz)
[60495.980163] ath5k phy0: gain calibration timeout (2472MHz)
[60496.436114] ath5k phy0: gain calibration timeout (2412MHz)
[60501.443371] ath5k phy0: gain calibration timeout (2412MHz)
[60501.928313] ath5k phy0: gain calibration timeout (2417MHz)
[60502.415065] ath5k phy0: gain calibration timeout (2422MHz)
[60502.898951] ath5k phy0: gain calibration timeout (2427MHz)
[60503.493566] ath5k phy0: gain calibration timeout (2432MHz)
[60504.091098] ath5k phy0: gain calibration timeout (2437MHz)
[60504.685973] ath5k phy0: gain calibration timeout (2442MHz)
[60505.171245] ath5k phy0: gain calibration timeout (2447MHz)
[60505.765487] ath5k phy0: gain calibration timeout (2452MHz)
[60506.367604] ath5k phy0: gain calibration timeout (2457MHz)
[60506.961540] ath5k phy0: gain calibration timeout (2462MHz)
[60507.449769] ath5k phy0: gain calibration timeout (2467MHz)
[60507.903215] ath5k phy0: gain calibration timeout (2472MHz)
[60508.355360] ath5k phy0: gain calibration timeout (2412MHz)
[60508.691737] ath5k phy0: gain calibration timeout (2412MHz)
[60509.297632] ath5k phy0: gain calibration timeout (2417MHz)
[60509.896574] ath5k phy0: gain calibration timeout (2422MHz)
[60510.394577] ath5k phy0: gain calibration timeout (2427MHz)
[60510.882154] ath5k phy0: gain calibration timeout (2432MHz)
[60511.574300] ath5k phy0: gain calibration timeout (2437MHz)
[60512.702272] ath5k phy0: gain calibration timeout (2447MHz)
[60513.302369] ath5k phy0: gain calibration timeout (2452MHz)
[60513.790676] ath5k phy0: gain calibration timeout (2457MHz)
[60514.276330] ath5k phy0: gain calibration timeout (2462MHz)
[60514.770836] ath5k phy0: gain calibration timeout (2467MHz)
[60515.222863] ath5k phy0: gain calibration timeout (2472MHz)
[60515.676394] ath5k phy0: gain calibration timeout (2412MHz)
[60520.681931] ath5k phy0: gain calibration timeout (2412MHz)
[60521.279722] ath5k phy0: gain calibration timeout (2417MHz)
[60521.876086] ath5k phy0: gain calibration timeout (2422MHz)
[60522.371185] ath5k phy0: gain calibration timeout (2427MHz)
[60522.968606] ath5k phy0: gain calibration timeout (2432MHz)
[60523.568069] ath5k phy0: gain calibration timeout (2437MHz)
[60524.169494] ath5k phy0: gain calibration timeout (2442MHz)
[60524.773294] ath5k phy0: gain calibration timeout (2447MHz)
[60525.375266] ath5k phy0: gain calibration timeout (2452MHz)
[60525.972287] ath5k phy0: gain calibration timeout (2457MHz)
[60526.571873] ath5k phy0: gain calibration timeout (2462MHz)
[60527.062237] ath5k phy0: gain calibration timeout (2467MHz)
[60527.518052] ath5k phy0: gain calibration timeout (2472MHz)
[60527.976102] ath5k phy0: gain calibration timeout (2412MHz)
[60532.975478] ath5k phy0: gain calibration timeout (2412MHz)
[60533.464671] ath5k phy0: gain calibration timeout (2417MHz)
[60534.065030] ath5k phy0: gain calibration timeout (2422MHz)
[60534.665327] ath5k phy0: gain calibration timeout (2427MHz)
[60535.153110] ath5k phy0: gain calibration timeout (2432MHz)
[60535.644071] ath5k phy0: gain calibration timeout (2437MHz)
[60536.132365] ath5k phy0: gain calibration timeout (2442MHz)
[60536.731563] ath5k phy0: gain calibration timeout (2447MHz)
[60537.327488] ath5k phy0: gain calibration timeout (2452MHz)
[60537.813358] ath5k phy0: gain calibration timeout (2457MHz)
[60538.788595] ath5k phy0: gain calibration timeout (2467MHz)
[60539.243956] ath5k phy0: gain calibration timeout (2472MHz)
[60539.700119] ath5k phy0: gain calibration timeout (2412MHz)

~$ uname -a
Linux buzz-dee-laptop 3.3.5-030305-generic #201205071254 SMP Mon May 7 16:56:02 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

Now I will try: http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.3.6-precise/