linux-kernel - [PATCH v2 09/17] staging/lirc_serial: Remove TSC-based timing

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Message-Id: <c95df47c5405b494d19d20b2852a9378c9f661f3.1434152603.git.luto@kernel.org>
Date:	Fri, 12 Jun 2015 16:44:49 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	Borislav Petkov <bp@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	Huang Rui <ray.huang@....com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Jarod Wilson <jarod@...sonet.com>, devel@...verdev.osuosl.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH v2 09/17] staging/lirc_serial: Remove TSC-based timing

It wasn't compiled in by default.  I suspect that the driver was and
still is broken, though -- it's calling udelay with a parameter
that's derived from loops_per_jiffy.

Cc: Jarod Wilson <jarod@...sonet.com>
Cc: devel@...verdev.osuosl.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 drivers/staging/media/lirc/lirc_serial.c | 63 ++------------------------------
 1 file changed, 4 insertions(+), 59 deletions(-)

diff --git a/drivers/staging/media/lirc/lirc_serial.c b/drivers/staging/media/lirc/lirc_serial.c
index dc7984455c3a..465796a686c4 100644
--- a/drivers/staging/media/lirc/lirc_serial.c
+++ b/drivers/staging/media/lirc/lirc_serial.c
@@ -327,9 +327,6 @@ static void safe_udelay(unsigned long usecs)
  * time
  */
 
-/* So send_pulse can quickly convert microseconds to clocks */
-static unsigned long conv_us_to_clocks;
-
 static int init_timing_params(unsigned int new_duty_cycle,
 		unsigned int new_freq)
 {
@@ -344,7 +341,6 @@ static int init_timing_params(unsigned int new_duty_cycle,
 	/* How many clocks in a microsecond?, avoiding long long divide */
 	work = loops_per_sec;
 	work *= 4295;  /* 4295 = 2^32 / 1e6 */
-	conv_us_to_clocks = work >> 32;
 
 	/*
 	 * Carrier period in clocks, approach good up to 32GHz clock,
@@ -357,10 +353,9 @@ static int init_timing_params(unsigned int new_duty_cycle,
 	pulse_width = period * duty_cycle / 100;
 	space_width = period - pulse_width;
 	dprintk("in init_timing_params, freq=%d, duty_cycle=%d, "
-		"clk/jiffy=%ld, pulse=%ld, space=%ld, "
-		"conv_us_to_clocks=%ld\n",
+		"clk/jiffy=%ld, pulse=%ld, space=%ld\n",
 		freq, duty_cycle, __this_cpu_read(cpu_info.loops_per_jiffy),
-		pulse_width, space_width, conv_us_to_clocks);
+		pulse_width, space_width);
 	return 0;
 }
 #else /* ! USE_RDTSC */
@@ -431,63 +426,14 @@ static long send_pulse_irdeo(unsigned long length)
 	return ret;
 }
 
-#ifdef USE_RDTSC
-/* Version that uses Pentium rdtsc instruction to measure clocks */
-
-/*
- * This version does sub-microsecond timing using rdtsc instruction,
- * and does away with the fudged LIRC_SERIAL_TRANSMITTER_LATENCY
- * Implicitly i586 architecture...  - Steve
- */
-
-static long send_pulse_homebrew_softcarrier(unsigned long length)
-{
-	int flag;
-	unsigned long target, start, now;
-
-	/* Get going quick as we can */
-	rdtscl(start);
-	on();
-	/* Convert length from microseconds to clocks */
-	length *= conv_us_to_clocks;
-	/* And loop till time is up - flipping at right intervals */
-	now = start;
-	target = pulse_width;
-	flag = 1;
-	/*
-	 * FIXME: This looks like a hard busy wait, without even an occasional,
-	 * polite, cpu_relax() call.  There's got to be a better way?
-	 *
-	 * The i2c code has the result of a lot of bit-banging work, I wonder if
-	 * there's something there which could be helpful here.
-	 */
-	while ((now - start) < length) {
-		/* Delay till flip time */
-		do {
-			rdtscl(now);
-		} while ((now - start) < target);
-
-		/* flip */
-		if (flag) {
-			rdtscl(now);
-			off();
-			target += space_width;
-		} else {
-			rdtscl(now); on();
-			target += pulse_width;
-		}
-		flag = !flag;
-	}
-	rdtscl(now);
-	return ((now - start) - length) / conv_us_to_clocks;
-}
-#else /* ! USE_RDTSC */
 /* Version using udelay() */
 
 /*
  * here we use fixed point arithmetic, with 8
  * fractional bits.  that gets us within 0.1% or so of the right average
  * frequency, albeit with some jitter in pulse length - Steve
+ *
+ * This should use ndelay instead.
  */
 
 /* To match 8 fractional bits used for pulse/space length */
@@ -520,7 +466,6 @@ static long send_pulse_homebrew_softcarrier(unsigned long length)
 	}
 	return (actual-length) >> 8;
 }
-#endif /* USE_RDTSC */
 
 static long send_pulse_homebrew(unsigned long length)
 {
-- 
2.4.2

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