Re: [kvm-unit-tests PATCH v3 7/9] s390x: css: msch, enable test

[Cornelia Huck <cohuck@redhat.com>]

On Fri,  6 Dec 2019 17:26:26 +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 | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/s390x/css.c b/s390x/css.c
> index 3d4a986..4c0031c 100644
> --- a/s390x/css.c
> +++ b/s390x/css.c
> @@ -58,11 +58,50 @@ static void test_enumerate(void)
>  	report("Tested %d devices, %d found", 1, scn, found);
>  }
>  
> +static void test_enable(void)
> +{
> +	struct pmcw *pmcw = &schib.pmcw;
> +	int cc;
> +
> +	if (!test_device_sid) {
> +		report_skip("No device");
> +		return;
> +	}
> +	/* Read the SCIB for this subchannel */

s/SCIB/SCHIB/

> +	cc = stsch(test_device_sid, &schib);
> +	if (cc) {
> +		report("stsch cc=%d", 0, 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) {
> +		report("msch cc=%d", 0, cc);

So you expect the subchannel to be idle? Probably true, especially as
QEMU has no reason to post an unsolicited interrupt for a test device.

> +		return;
> +	}
> +
> +	/* Read the SCHIB again to verify the enablement */
> +	cc = stsch(test_device_sid, &schib);
> +	if (cc) {
> +		report("stsch cc=%d", 0, cc);
> +		return;
> +	}
> +	if (!(pmcw->flags & PMCW_ENABLE)) {
> +		report("Enable failed. pmcw: %x", 0, pmcw->flags);

This check is fine when running under KVM. If this test is modified to
run under z/VM in the future, you probably should retry here: I've seen
the enable bit 'stick' only after the second msch() there.

> +		return;
> +	}
> +	report("Tested", 1);
> +}
> +
>  static struct {
>  	const char *name;
>  	void (*func)(void);
>  } tests[] = {
>  	{ "enumerate (stsch)", test_enumerate },
> +	{ "enable (msch)", test_enable },
>  	{ NULL, NULL }
>  };
>