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

Cornelia Huck
2019-12-12T12:01:21Z

On Wed, 11 Dec 2019 16:46:08 +0100
Pierre Morel <pmorel@linux.ibm.com> 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@linux.ibm.com>
> ---
> 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?

> +
> 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.

> + 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, and you probably should not delay on success?

> + } 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?

> +
> + if (!(pmcw->flags & PMCW_ENABLE)) {
> + report(0, "Enable failed. pmcw: %x", pmcw->flags);
> + return;
> + }
> + report(1, "Tested");
> +}
> +
> static struct {
> const char *name;
> void (*func)(void);
> } tests[] = {
> { "enumerate (stsch)", test_enumerate },
> + { "enable (msch)", test_enable },
> { NULL, NULL }
> };
>