linux-kernel - [PATCH 4.14 030/343] switchtec: Remove immediate status check after submitting MRPC command

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Date:   Fri, 24 Jan 2020 10:27:28 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kelvin Cao <kelvin.cao@...rochip.com>,
        Wesley Sheng <wesley.sheng@...rochip.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 030/343] switchtec: Remove immediate status check after submitting MRPC command

From: Kelvin Cao <kelvin.cao@...rochip.com>

[ Upstream commit 526180408b815aa7b96fd48bd23cdd33ef04e38e ]

After submitting a Firmware Download MRPC command, Switchtec firmware will
delay Management EP BAR MemRd TLP responses by more than 10ms.  This is a
firmware limitation.  Delayed MemRd completions are a problem for systems
with a low Completion Timeout (CTO).

The current driver checks the MRPC status immediately after submitting an
MRPC command, which results in a delayed MemRd completion that may cause a
Completion Timeout.

Remove the immediate status check and rely on the check after receiving an
interrupt or timing out.

This is only a software workaround to the READ issue and a proper fix of
this should be done in firmware.

Fixes: 080b47def5e5 ("MicroSemi Switchtec management interface driver")
Signed-off-by: Kelvin Cao <kelvin.cao@...rochip.com>
Signed-off-by: Wesley Sheng <wesley.sheng@...rochip.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Reviewed-by: Logan Gunthorpe <logang@...tatee.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/pci/switch/switchtec.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
index 0941555b84a52..73dba2739849b 100644
--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -399,10 +399,6 @@ static void mrpc_cmd_submit(struct switchtec_dev *stdev)
 		    stuser->data, stuser->data_len);
 	iowrite32(stuser->cmd, &stdev->mmio_mrpc->cmd);
 
-	stuser->status = ioread32(&stdev->mmio_mrpc->status);
-	if (stuser->status != SWITCHTEC_MRPC_STATUS_INPROGRESS)
-		mrpc_complete_cmd(stdev);
-
 	schedule_delayed_work(&stdev->mrpc_timeout,
 			      msecs_to_jiffies(500));
 }
-- 
2.20.1