[PATCH v2] drivers: scmi: Add completion timeout handling for raw mode transfers

[Artem Shimko <a.shimko.dev@gmail.com>]

Fix race conditions in SCMI raw mode implementation by adding proper
completion timeout handling. Multiple tests in the SCMI test suite
were failing due to early clearing of SCMI_XFER_FLAG_IS_RAW flag in
scmi_xfer_raw_put() function.

TRANS=raw
PROTOCOLS=base,clock,power_domain,performance,system_power,sensor,
voltage,reset,powercap,pin_control VERBOSE=5

The root cause:
Tests were failing on poll() system calls with this condition:
    if (!raw || (idx == SCMI_RAW_REPLY_QUEUE && !SCMI_XFER_IS_RAW(xfer)))
        return;

The SCMI_XFER_FLAG_IS_RAW flag was being cleared prematurely before
the transfer completion was properly acknowledged, causing the poll
to return on timeout and tests to fail.

Fix ensures:
- Proper synchronization between transfer completion and flag clearing
- Stable test execution by maintaining correct flag states

An example of a random test failure:
 817: Voltage get ext name for invalid domain
     [Check 1] Get extended name for invalid domain
       MSG HDR        : 0x04585c09
       NUM PARAM      : 1
       PARAMETER[00]  : 0x0000000c
       CHECK STATUS   : PASSED [SCMI_NOT_FOUND_ERR]
       CHECK HEADER   : PASSED [0x04585c09]
       RETURN COUNT   : 0
       NUM DOMAINS    : 11
       VOLTAGE DOMAIN : 0
     [Check 2] Get extended name for unsupp. domain
       MSG HDR        : 0x045c5c09
       NUM PARAM      : 1
       PARAMETER[00]  : 0x00000000
       CHECK STATUS   : FAILED
           EXPECTED   : SCMI_NOT_FOUND_ERR
           RECEIVED   : SCMI_GENERIC_ERROR  : NON CONFORMANT

After making these changes, the tests stopped failing.

$mount -t debugfs none /sys/kernel/debug
$scmi_test_agent
[  127.865032] arm-scmi arm-scmi.1.auto: Resetting SCMI Raw stack.
[  128.360503] arm-scmi arm-scmi.1.auto: Using Base channel for protocol 0x12
$tail -n 6 arm_scmi_test_log.txt
****************************************************
  TOTAL TESTS: 167    PASSED: 120    FAILED: 0    SKIPPED: 47
****************************************************

An ftrace log with of passed test:
0)               |  scmi_rx_callback()
0)               |    scmi_raw_message_report()
7)               |    scmi_xfer_raw_wait_for_message_response()
7) + 22.000 us   |      scmi_wait_for_reply();
0)               |        /* scmi_raw_message_report*/
7)               |    scmi_xfer_raw_put()

An ftrace log with of failed test:
0)               |  scmi_rx_callback() {
0)               |    scmi_raw_message_report()
5)               |    scmi_xfer_raw_wait_for_message_response()
5) ! 383.000 us  |      scmi_wait_for_reply();
5)               |    scmi_xfer_raw_put() {
0)               |  /* scmi_raw_message_report*/

Link [1] https://gitlab.arm.com/tests/scmi-tests/-/releases

Fixes: 3095a3e25d8f7 (firmware: arm_scmi: Add xfer helpers to provide raw access)
Suggested-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Artem Shimko <a.shimko.dev@gmail.com>
---
Hi Cristian,

Good point about CONFIG_ARM_SCMI_RAW_MODE_SUPPORT_COEX. 

I can confirm this setting doesn't impact the test failures in my environment.
The issue reproduces consistently with COEX both enabled and disabled.

Thank you!

Best regards,
Artem Shimko

ChangeLog:
  v1:
    * https://lore.kernel.org/arm-scmi/20250929142856.540590-1-a.shimko.dev@gmail.com/
  v2:
    * Use simpler approach suggested by Cristian Marussi
    * Clear all xfer flags in __scmi_xfer_put() under spinlock protection  
    * Add Fixes tag as requested
    * Drop completion timeout mechanism from v1

 drivers/firmware/arm_scmi/driver.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index bd56a877fdfc..0976bfdbb44b 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -821,6 +821,7 @@ __scmi_xfer_put(struct scmi_xfers_info *minfo, struct scmi_xfer *xfer)
 
 			scmi_dec_count(info->dbg->counters, XFERS_INFLIGHT);
 		}
+		xfer->flags = 0;
 		hlist_add_head(&xfer->node, &minfo->free_xfers);
 	}
 	spin_unlock_irqrestore(&minfo->xfer_lock, flags);
@@ -839,8 +840,6 @@ void scmi_xfer_raw_put(const struct scmi_handle *handle, struct scmi_xfer *xfer)
 {
 	struct scmi_info *info = handle_to_scmi_info(handle);
 
-	xfer->flags &= ~SCMI_XFER_FLAG_IS_RAW;
-	xfer->flags &= ~SCMI_XFER_FLAG_CHAN_SET;
 	return __scmi_xfer_put(&info->tx_minfo, xfer);
 }
 
-- 
2.43.0