1. 11 Feb, 2016 1 commit
  2. 08 Feb, 2016 1 commit
    • Linus Walleij's avatar
      ARM: 8517/1: ICST: avoid arithmetic overflow in icst_hz() · 5070fb14
      Linus Walleij authored
      When trying to set the ICST 307 clock to 25174000 Hz I ran into
      this arithmetic error: the icst_hz_to_vco() correctly figure out
      DIVIDE=2, RDW=100 and VDW=99 yielding a frequency of
      25174000 Hz out of the VCO. (I replicated the icst_hz() function
      in a spreadsheet to verify this.)
      
      However, when I called icst_hz() on these VCO settings it would
      instead return 4122709 Hz. This causes an error in the common
      clock driver for ICST as the common clock framework will call
      .round_rate() on the clock which will utilize icst_hz_to_vco()
      followed by icst_hz() suggesting the erroneous frequency, and
      then the clock gets set to this.
      
      The error did not manifest in the old clock framework since
      this high frequency was only used by the CLCD, which calls
      clk_set_rate() without first calling clk_round_rate() and since
      the old clock framework would not call clk_round_rate() before
      setting the frequency, the correct values propagated into
      the VCO.
      
      After some experimenting I figured out that it was due to a simple
      arithmetic overflow: the divisor for 24Mhz reference frequency
      as reference becomes 24000000*2*(99+8)=0x132212400 and the "1"
      in bit 32 overflows and is lost.
      
      But introducing an explicit 64-by-32 bit do_div() and casting
      the divisor into (u64) we get the right frequency back, and the
      right frequency gets set.
      
      Tested on the ARM Versatile.
      
      Cc: stable@vger.kernel.org
      Cc: linux-clk@vger.kernel.org
      Cc: Pawel Moll <pawel.moll@arm.com>
      Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
      Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
      5070fb14
  3. 27 Jan, 2016 1 commit
  4. 26 Jan, 2016 1 commit
  5. 24 Jan, 2016 36 commits