Re: [kvm-unit-tests PATCH v1 1/6] s390x: lib: css: disabling a subchannel

[Janosch Frank <frankja@linux.ibm.com>]

On 3/18/21 2:26 PM, Pierre Morel wrote:
> Some tests require to disable a subchannel.
> Let's implement the css_disable() function.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>

Looks ok, minor nits below.

> ---
>  lib/s390x/css.h     |  1 +
>  lib/s390x/css_lib.c | 69 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 70 insertions(+)
> 
> diff --git a/lib/s390x/css.h b/lib/s390x/css.h
> index 7e3d261..b0de3a3 100644
> --- a/lib/s390x/css.h
> +++ b/lib/s390x/css.h
> @@ -284,6 +284,7 @@ int css_enumerate(void);
>  #define IO_SCH_ISC      3
>  int css_enable(int schid, int isc);
>  bool css_enabled(int schid);
> +int css_disable(int schid);
>  
>  /* Library functions */
>  int start_ccw1_chain(unsigned int sid, struct ccw1 *ccw);
> diff --git a/lib/s390x/css_lib.c b/lib/s390x/css_lib.c
> index efc7057..f8db205 100644
> --- a/lib/s390x/css_lib.c
> +++ b/lib/s390x/css_lib.c
> @@ -186,6 +186,75 @@ bool css_enabled(int schid)
>  	}
>  	return true;
>  }
> +
> +/*
> + * css_disable: disable the subchannel
> + * @schid: Subchannel Identifier
> + * Return value:
> + *   On success: 0
> + *   On error the CC of the faulty instruction
> + *      or -1 if the retry count is exceeded.
> + */
> +int css_disable(int schid)
> +{
> +	struct pmcw *pmcw = &schib.pmcw;
> +	int retry_count = 0;
> +	int cc;
> +
> +	/* Read the SCHIB for this subchannel */
> +	cc = stsch(schid, &schib);
> +	if (cc) {
> +		report_info("stsch: sch %08x failed with cc=%d", schid, cc);
> +		return cc;
> +	}
> +
> +	if (!(pmcw->flags & PMCW_ENABLE)) {
> +		report_info("stsch: sch %08x already disabled", schid);
> +		return 0;
> +	}
> +
> +retry:
> +	/* Update the SCHIB to disable the subchannel */
> +	pmcw->flags &= ~PMCW_ENABLE;
> +
> +	/* Tell the CSS we want to modify the subchannel */
> +	cc = msch(schid, &schib);
> +	if (cc) {
> +		/*
> +		 * If the subchannel is status pending or
> +		 * if a function is in progress,
> +		 * we consider both cases as errors.
> +		 */

Weird indentation, the lines should be longer, no?

> +		report_info("msch: sch %08x failed with cc=%d", schid, cc);
> +		return cc;
> +	}
> +
> +	/*
> +	 * Read the SCHIB again to verify the enablement
> +	 */

Can be one line

> +	cc = stsch(schid, &schib);
> +	if (cc) {
> +		report_info("stsch: updating sch %08x failed with cc=%d",
> +			    schid, cc);
> +		return cc;
> +	}
> +
> +	if (!(pmcw->flags & PMCW_ENABLE)) {
> +		if (retry_count)
> +			report_info("stsch: sch %08x successfully disabled after %d retries",
> +				    schid, retry_count);
> +		return 0;
> +	}
> +
> +	if (retry_count++ < MAX_ENABLE_RETRIES) {
> +		mdelay(10); /* the hardware was not ready, give it some time */

Personally I dislike comments at the end of lines except for
constant/variable comments. Just put it before the delay.

> +		goto retry;
> +	}
> +
> +	report_info("msch: modifying sch %08x failed after %d retries. pmcw flags: %04x",
> +		    schid, retry_count, pmcw->flags);
> +	return -1;
> +}
>  /*
>   * css_enable: enable the subchannel with the specified ISC
>   * @schid: Subchannel Identifier
>