Re: [kvm-unit-tests PATCH v4 7/9] s390x: css: msch, enable test

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On 2019-12-12 13:01, Cornelia Huck wrote:
On Wed, 11 Dec 2019 16:46:08 +0100
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

A second step when testing the channel subsystem is to prepare a channel
for use.
This includes:
- Get the current SubCHannel Information Block (SCHIB) using STSCH
- Update it in memory to set the ENABLE bit
- Tell the CSS that the SCHIB has been modified using MSCH
- Get the SCHIB from the CSS again to verify that the subchannel is
   enabled.

This tests the success of the MSCH instruction by enabling a channel.

Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
  s390x/css.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 65 insertions(+)

diff --git a/s390x/css.c b/s390x/css.c
index dfab35f..b8824ad 100644
--- a/s390x/css.c
+++ b/s390x/css.c
@@ -19,12 +19,24 @@
  #include <asm/time.h>
#include <css.h>
+#include <asm/time.h>
#define SID_ONE 0x00010000 static struct schib schib;
  static int test_device_sid;
+static inline void delay(unsigned long ms)
+{
+	unsigned long startclk;
+
+	startclk = get_clock_ms();
+	for (;;) {
+		if (get_clock_ms() - startclk > ms)
+			break;
+	}
+} >
Would this function be useful for other callers as well? I.e., should
it go into a common header?

Yes, I wanted to put it in the new time.h with the get_clock_ms() but did not since I already got the RB. I also did not want to add a patch to the series, but since you ask, I can put it in a separate patch to keep the RB and to add it in the time.h


+
  static void test_enumerate(void)
  {
  	struct pmcw *pmcw = &schib.pmcw;
@@ -64,11 +76,64 @@ out:
  	report(1, "Devices, tested: %d, I/O type: %d", scn, scn_found);
  }
+static void test_enable(void)
+{
+	struct pmcw *pmcw = &schib.pmcw;
+		int count = 0;

Odd indentation.

indeed!


+	int cc;
+
+	if (!test_device_sid) {
+		report_skip("No device");
+		return;
+	}
+	/* Read the SCHIB for this subchannel */
+	cc = stsch(test_device_sid, &schib);
+	if (cc) {
+		report(0, "stsch cc=%d", cc);
+		return;
+	}
+
+	/* Update the SCHIB to enable the channel */
+	pmcw->flags |= PMCW_ENABLE;
+
+	/* Tell the CSS we want to modify the subchannel */
+	cc = msch(test_device_sid, &schib);
+	if (cc) {
+		/*
+		 * If the subchannel is status pending or
+		 * if a function is in progress,
+		 * we consider both cases as errors.
+		 */
+		report(0, "msch cc=%d", cc);
+		return;
+	}
+
+	/*
+	 * Read the SCHIB again to verify the enablement
+	 * insert a little delay and try 5 times.
+	 */
+	do {
+		cc = stsch(test_device_sid, &schib);
+		if (cc) {
+			report(0, "stsch cc=%d", cc);
+			return;
+		}
+		delay(10);

That's just a short delay to avoid a busy loop, right? msch should be
immediate,

Thought you told to me that it may not be immediate in zVM did I misunderstand?

and you probably should not delay on success?

yes, it is not optimized, I can test PMCW_ENABLE in the loop this way we can see if, in the zVM case we need to do retries or not.



+	} while (!(pmcw->flags & PMCW_ENABLE) && count++ < 5);

How is this supposed to work? Doesn't the stsch overwrite the control
block again, so you need to re-set the enable bit before you retry?

I do not think so, there is no msch() in the loop.
Do I miss something?

Thanks for the review,
Regards,

Pierre


--
Pierre Morel
IBM Lab Boeblingen




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