On Fri, 23 Nov 2012 14:21:58 +0200, Jani Nikula <[email protected]> wrote: > On Fri, 23 Nov 2012, Chris Wilson <[email protected]> wrote: > > Some devices may respond very slowly and only flag that the reply is > > pending within the first 15us response window. Be kind to such devices > > and wait a further 15ms, before checking for the pending reply. This > > moves the existing special case delay of 30ms down from the detection > > routine into the common path and pretends to explain it... > > > > v2: Simplify the loop constructs as suggested by Jani Nikula. > > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=36997 > > Signed-off-by: Chris Wilson <[email protected]> > > --- > > drivers/gpu/drm/i915/intel_sdvo.c | 31 +++++++++++++++++++------------ > > 1 file changed, 19 insertions(+), 12 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/intel_sdvo.c > > b/drivers/gpu/drm/i915/intel_sdvo.c > > index d85ebb0..cff3c0b 100644 > > --- a/drivers/gpu/drm/i915/intel_sdvo.c > > +++ b/drivers/gpu/drm/i915/intel_sdvo.c > > @@ -509,7 +509,7 @@ out: > > static bool intel_sdvo_read_response(struct intel_sdvo *intel_sdvo, > > void *response, int response_len) > > { > > - u8 retry = 5; > > + u8 retry = 15; /* 5 quick checks, followed by 10 long checks */ > > u8 status; > > int i; > > > > @@ -522,14 +522,27 @@ static bool intel_sdvo_read_response(struct > > intel_sdvo *intel_sdvo, > > * command to be complete. > > * > > * Check 5 times in case the hardware failed to read the docs. > > + * > > + * Also beware that the first response by many devices is to > > + * reply PENDING and stall for time. TVs are notorious for > > + * requiring longer than specified to complete their replies. > > + * Originally (in the DDX long ago), the delay was only ever 15ms > > + * with an additional delay of 30ms applied for TVs added later after > > + * many experiments. To accommodate both sets of delays, we do a > > + * sequence of slow checks if the device is falling behind and fails > > + * to reply within 5*15µs. > > */ > > if (!intel_sdvo_read_byte(intel_sdvo, > > SDVO_I2C_CMD_STATUS, > > &status)) > > goto log_fail; > > > > - while (status == SDVO_CMD_STATUS_PENDING && retry--) { > > - udelay(15); > > + while (status == SDVO_CMD_STATUS_PENDING && --retry) { > > Hey, why did you switch from post to pre decrement? It will now retry > only retry-1 times. Or is this about the semantics of retries vs. tries? > ;)
Because on the last go through, inside the loop retry would be 255 and we would not get the final 15ms sleep. -Chris -- Chris Wilson, Intel Open Source Technology Centre
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