linux-kernel - [PATCH 1/12 v2] switchtec: Remove immediate status check after submit a MRPC command

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Date:   Thu, 27 Sep 2018 05:57:19 +0000
From:   <Wesley.Sheng@...rochip.com>
To:     <logang@...tatee.com>, <kurt.schwemmer@...rosemi.com>,
        <Kurt.Schwemmer@...rochip.com>, <bhelgaas@...gle.com>
CC:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <Wesley.Sheng@...rochip.com>, <Kelvin.Cao@...rochip.com>
Subject: [PATCH 1/12 v2] switchtec: Remove immediate status check after submit
 a MRPC command

After submit a Firmware Download (Download sub-command) MRPC
command, Switchtec firmware refuses to response any management 
EP's BAR access until current flash programming finished.
During this time, a READ TLP to the gas area in the BAR of the
management EP will complete with significant delay like more than 
10ms.
It's a Switchtec firmware limitation that READ requests cannot get
prompt service during firmware download.
The delayed completion of READ TLP would be a problem on some system
 which is sensitive to READ timeout.
Current driver check status immediately after submit a MRPC command,
which triggers READ TLP to the gas area in the BAR of the management EP.
Also, other processes or functions, like NTB, would also trigger READ TLP by
accessing the GAS.
To avoid this, the immediate check of status is removed in this patch, and
driver delays the status check to the occurrence of MSIx or MRPC timeout.
In the meantime, user must not initiate any gas access during a firmware
download.
Also, any process that issues MRPC command will be affected by the delay
in this patch.
However, this is only a software workaround to the READ issue in firmware
download. A complete fix of this should happen in firmware.

Note: For NTB function, the memory window access is handled by Switchtec
hardware. So it's not affected by this firmware limitation. But the other GAS
access which is handled by Switchtec firmware is are affected by this firmware
limitation.

Signed-off-by: Kelvin Cao <Kelvin.Cao@...rochip.com>
Signed-off-by: Wesley Sheng <Wesley.sheng@...rochip.com>

---
 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 4591f15..b759228 100644
--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -142,10 +142,6 @@ 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));
 }
--
2.7.4