[PATCH V2 04/16] smartpqi: close write read holes

From: Don Brace <don.brace@microchip.com>
To: <Kevin.Barnett@microchip.com>, <scott.teel@microchip.com>,
	<Justin.Lindley@microchip.com>, <scott.benesh@microchip.com>,
	<gerry.morong@microchip.com>, <mahesh.rajashekhara@microchip.com>,
	<mike.mcgowen@microchip.com>, <murthy.bhat@microchip.com>,
	<kumar.meiyappan@microchip.com>, <hch@infradead.org>,
	<jejb@linux.vnet.ibm.com>, <joseph.szczypek@hpe.com>,
	<POSWALD@suse.com>
Cc: <linux-scsi@vger.kernel.org>
Subject: [PATCH V2 04/16] smartpqi: close write read holes
Date: Fri, 8 Jul 2022 13:47:05 -0500	[thread overview]
Message-ID: <165730602555.177165.11181012469428348394.stgit@brunhilda> (raw)
In-Reply-To: <165730597930.177165.11663580730429681919.stgit@brunhilda>

From: Mike McGowen <Mike.McGowen@microchip.com>

Insert a minimum 1 millisecond delay after writing to a register before
reading from it.

SIS and PQI registers that can be both written to and read from can
return stale data if read from too soon after having been written to.

There is no read/write ordering or hazard detection on the inbound path
to the MSGU from the PCIe bus, therefore reads could pass writes.

Reviewed-by: Scott Teel <scott.teel@microchip.com>
Co-developed-by: Kevin Barnett <kevin.barnett@microchip.com>
Signed-off-by: Kevin Barnett <kevin.barnett@microchip.com>
Co-developed-by: Mike McGowen <mike.mcgowen@microchip.com>
Signed-off-by: Mike McGowen <mike.mcgowen@microchip.com>
Signed-off-by: Don Brace <don.brace@microchip.com>
---
 drivers/scsi/smartpqi/smartpqi_sis.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/scsi/smartpqi/smartpqi_sis.c b/drivers/scsi/smartpqi/smartpqi_sis.c
index afc27adf68e9..2b99b6e9cd71 100644
--- a/drivers/scsi/smartpqi/smartpqi_sis.c
+++ b/drivers/scsi/smartpqi/smartpqi_sis.c
@@ -194,6 +194,7 @@ static int sis_send_sync_cmd(struct pqi_ctrl_info *ctrl_info,
 
 	/* Disable doorbell interrupts by masking all interrupts. */
 	writel(~0, &registers->sis_interrupt_mask);
+	usleep_range(1000, 2000);
 
 	/*
 	 * Force the completion of the interrupt mask register write before
@@ -383,6 +384,7 @@ static int sis_wait_for_doorbell_bit_to_clear(
 static inline int sis_set_doorbell_bit(struct pqi_ctrl_info *ctrl_info, u32 bit)
 {
 	writel(bit, &ctrl_info->registers->sis_host_to_ctrl_doorbell);
+	usleep_range(1000, 2000);
 
 	return sis_wait_for_doorbell_bit_to_clear(ctrl_info, bit);
 }
@@ -423,6 +425,7 @@ int sis_reenable_sis_mode(struct pqi_ctrl_info *ctrl_info)
 void sis_write_driver_scratch(struct pqi_ctrl_info *ctrl_info, u32 value)
 {
 	writel(value, &ctrl_info->registers->sis_driver_scratch);
+	usleep_range(1000, 2000);
 }
 
 u32 sis_read_driver_scratch(struct pqi_ctrl_info *ctrl_info)

