linux-kernel - [PATCH -next 2/2] i2c: designware: Add support for new SoCs in AMDPSP driver

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Date:   Fri, 17 Mar 2023 13:18:34 -0600
From:   Mark Hasemeyer <markhas@...omium.org>
To:     jsd@...ihalf.com
Cc:     andriy.shevchenko@...ux.intel.com, jarkko.nikula@...ux.intel.com,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        mario.limonciello@....com, rrangel@...omium.org,
        upstream@...ihalf.com, wsa@...nel.org, dabros@...gle.com
Subject: [PATCH -next 2/2] i2c: designware: Add support for new SoCs in AMDPSP driver

-	/* Status field in command-response buffer is updated by PSP */
-	status = READ_ONCE(req->hdr.status);
+	if (req) {
+		/* Status field in command-response buffer is updated by PSP */
+		status = READ_ONCE(req->hdr.status);
+	} else {
+		status = psp_smn_read(PSP_MBOX_CMD_OFFSET, &status);
+		status &= ~PSP_MBOX_FIELDS_READY;
+	}

The value of the mbox cmd register is getting clobbered by the return value
from psp_smn_read. This can cause bus arbitration to fail as the driver will
think it can grab the bus when it's actually in use by the PSP.