Re: [PATCH v1 4/4] s390x: Testing the Subchannel I/O read

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On 2019-11-13 14:05, Cornelia Huck wrote:
On Wed, 13 Nov 2019 13:23:19 +0100
Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:

This simple test test the I/O reading by the SUB Channel by:
- initializing the Channel SubSystem with predefined CSSID:
   0xfe000000 CSSID for a Virtual CCW
0 should be fine with recent QEMU versions as well, I guess?
Right



   0x00090000 SSID for CCW-PONG
subchannel id, or subchannel set id?

hum, only part of, I had SSID (Subchannel Set ID) 4 (a.k.a m bit) + Bit 47  =1

But as you said, I can use CSSID 0 and m = 0 which makes:

Subsystem Identification word = 0x00010000



- initializing the ORB pointing to a single READ CCW
Out of curiosity: Would using a NOP also be an option?

It will work but will not be handled by this device, css.c intercept it in sch_handle_start_func_virtual.

AFAIU If we want to have a really good testing environment, for driver testing for exemple, then it would be interesting to add a new do_subchannel_work callback like do_subchannel_work_emulation along with the _virtual and _paththrough variantes.

Having a dedicated callback for emulation, we can answer to any CSS instructions and SSCH commands, including NOP and TIC.

My goal here was to quickly develop a device answering to some basic READ/WRITE command to start memory transfers from inside a guest without Linux and without implementing VIRTIO in KVM tests.




- starts the STSH command with the ORB
s/STSH/SSCH/ ?

:) yes, thanks



- Expect an interrupt
- writes the read data to output

The test implements lots of traces when DEBUG is on and
tests if memory above the stack is corrupted.

Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
  lib/s390x/css.h      | 244 +++++++++++++++++++++++++++++++++++++++++++++++++++
  lib/s390x/css_dump.c | 141 +++++++++++++++++++++++++++++
  s390x/Makefile       |   2 +
  s390x/css.c          | 222 ++++++++++++++++++++++++++++++++++++++++++++++
  s390x/unittests.cfg  |   4 +
  5 files changed, 613 insertions(+)
  create mode 100644 lib/s390x/css.h
  create mode 100644 lib/s390x/css_dump.c
  create mode 100644 s390x/css.c

diff --git a/lib/s390x/css.h b/lib/s390x/css.h
new file mode 100644
index 0000000..a7c42fd
--- /dev/null
+++ b/lib/s390x/css.h
(...)

+static inline int rsch(unsigned long schid)
I don't think anyone has tried rsch with QEMU before; sounds like a
good idea to test this :)

With an do_subchannel_work_emulation() callback?



+{
+	register unsigned long reg1 asm("1") = schid;
+	int ccode;
+
+	asm volatile(
+		"	rsch\n"
+		"	ipm	%0\n"
+		"	srl	%0,28"
+		: "=d" (ccode)
+		: "d" (reg1)
+		: "cc");
+	return ccode;
+}
+
+static inline int rchp(unsigned long chpid)
Anything useful we can test here?

Not for now.

I certainly can reduce the size of the file by removing the unused CSS instructions calls.

...snip...
+
+static void enable_io_irq(void)
+{
+	set_io_irq_subclass_mask(0x00000000ff000000);
So, you always enable all iscs? Maybe add a comment?

OK, is just a lazy option to get IRQ for this test.

Right, I add a comment.



+	set_system_mask(PSW_PRG_MASK >> 56);
+}
+
+void handle_io_int(sregs_t *regs)
+{
+	int ret = 0;
+
+	DBG("IO IRQ: subsys_id_word=%08x", lowcore->subsys_id_word);
+	DBG("......: io_int_parm   =%08x", lowcore->io_int_param);
+	DBG("......: io_int_word   =%08x", lowcore->io_int_word);
+	ret = tsch(lowcore->subsys_id_word, &irb);
+	dump_irb(&irb);
+	if (ret)
+		DBG("......: tsch retval %d", ret);
+	DBG("IO IRQ: END");
+}
+
+static void set_schib(struct schib *sch)
+{
+	struct pmcw *p = &sch->pmcw;
+
+	p->intparm = 0xdeadbeef;
+	p->devnum = 0xc0ca;
+	p->lpm = 0x80;
+	p->flags = 0x3081;
Use #defines instead of magic numbers?

OK



+	p->chpid[7] = 0x22;
+	p->pim = 0x0f;
+	p->pam = 0x0f;
+	p->pom = 0x0f;
+	p->lpm = 0x0f;
+	p->lpum = 0xaa;
+	p->pnom = 0xf0;
+	p->mbi = 0xaa;
+	p->mbi = 0xaaaa;
Many of these fields are not supposed to be modifiable by the program
-- do you want to check what you get back after msch?

Also, you set mbi twice ;) (And for it to actually have any effect,
you'd have to execute SET CHANNEL MONITOR, no?)

Yes, it was for me to check what happens but I should remove most of these field initialization.

As you said they are not modifiable by the program.

Will clean this.




+}
+
+static void css_enable(void)
+{
+	int ret;
+
+	ret = stsch(CSSID_PONG, &schib);
+	if (ret)
+		DBG("stsch: %x\n", ret);
+	dump_schib(&schib);
+	set_schib(&schib);
+	dump_schib(&schib);
+	ret = msch(CSSID_PONG, &schib);
+	if (ret)
+		DBG("msch : %x\n", ret);
+}
+
+/* These two definitions are part of the QEMU PONG interface */
+#define PONG_WRITE 0x21
+#define PONG_READ  0x22
Ah, so it's not a plain read/write, but a specialized one? Mention that
in the patch description?

+
+static int css_run(int fake)
+{
+	struct orb *p = orb;
I'd maybe call that variable 'orb' instead; at a glance, I was confused
what you did with the pmcw below, until I realized that it's the orb :)

OK, is clearly better to use orb.


Thanks,

Pierre


--
Pierre Morel
IBM Lab Boeblingen




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