On Thu, Mar 8, 2018 at 2:12 PM, Joel Stanley <j...@jms.id.au> wrote: > Hi Eddie, > > On Thu, Mar 8, 2018 at 3:06 AM, Eddie James <eaja...@linux.vnet.ibm.com> > wrote: >> According to the Aspeed specification, the reset and enable sequence >> should be done when the clock is stopped. The specification doesn't >> define behavior if the reset is done while the clock is enabled. >> >> From testing on the AST2500, the LPC Controller has problems if the >> clock is reset while enabled. >> >> Therefore, check whether the clock is enabled or not before performing >> the reset and enable sequence in the Aspeed clock driver. >> >> Signed-off-by: Eddie James <eaja...@linux.vnet.ibm.com> >> --- >> drivers/clk/clk-aspeed.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/drivers/clk/clk-aspeed.c b/drivers/clk/clk-aspeed.c >> index 9f7f931..a13054d 100644 >> --- a/drivers/clk/clk-aspeed.c >> +++ b/drivers/clk/clk-aspeed.c >> @@ -212,6 +212,12 @@ static int aspeed_clk_enable(struct clk_hw *hw) >> u32 clk = BIT(gate->clock_idx); >> u32 rst = BIT(gate->reset_idx); >> u32 enval; >> + u32 reg; >> + >> + /* Only reset/enable/unreset if clock is stopped */ >> + regmap_read(gate->map, ASPEED_CLK_STOP_CTRL, ®); >> + if (!(reg & clk)) >> + return 0; > > This doesn't generalise to all of the clocks, as some clocks use set > to disable. Perhaps we could do something like this: > > /* Only reset/enable/unreset if clock is stopped. The LPC clock > on ast2500 has issues otherwise */
We've seen this on both the ast2400 and ast2500, so if you do take my suggestion perhaps just say "The LPC clock has issues otherwise". > enval = (gate->flags & CLK_GATE_SET_TO_DISABLE) ? 0 : clk; > regmap_read(gate->map, ASPEED_CLK_STOP_CTRL, ®); > if ((reg & clk) == enval) { > spin_unlock_irqrestore(gate->lock, flags); > return 0; > } > > I think we should also do this operation under the lock. > > Please cc Ryan Chen <ryan_c...@aspeedtech.com> so he can confirm that > this workaround is valid, and credit Lei who spent a lot of time > investigating this issue. Perhaps "Root-caused-by". > > Cheers, > > Joel