netdev - [PATCH 09/10] staging: wfx: ensure HIF request has been sent before polling

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Message-Id: <20220225112405.355599-10-Jerome.Pouiller@silabs.com>
Date:   Fri, 25 Feb 2022 12:24:04 +0100
From:   Jerome Pouiller <Jerome.Pouiller@...abs.com>
To:     linux-wireless@...r.kernel.org, Kalle Valo <kvalo@...nel.org>
Cc:     devel@...verdev.osuosl.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jérôme Pouiller 
        <jerome.pouiller@...abs.com>
Subject: [PATCH 09/10] staging: wfx: ensure HIF request has been sent before polling

From: Jérôme Pouiller <jerome.pouiller@...abs.com>

wfx_bh_request_tx() send HIF request asynchronously through bh_work().
Then the caller will run wfx_bh_poll_irq() to poll the answer.

However it useless to burn CPU cycles for the polling while the request
has yet been sent. Worse, wfx_bh_poll_irq() may get the CPU and prevent
wfx_bh_request_tx() to run. This problem has been observed on mono core
architecture.

This first exchange is correct:
    kworker/u2:1-24    [000] ....    : io_read32: CONTROL: 00003000
    kworker/u2:1-24    [000] ....    : io_read32: CONTROL: 00003000
    kworker/u2:1-24    [000] ....    : io_read32: CONTROL: 00003004
    kworker/u2:1-24    [000] ....    : io_read32: CONTROL: 00003004
    kworker/0:1H-40    [000] ....    : io_read: QUEUE: 08 00 09 0c 00 00 00 00 3a 7b 00 30 (12 bytes)
    kworker/0:1H-40    [000] ....    : piggyback: CONTROL: 00003000
    kworker/0:1H-40    [000] ....    : hif_recv: 0:2:CNF_CONFIGURATION: 00 00 00 00 (8 bytes)
    kworker/0:1H-40    [000] ....    : io_read32: CONFIG: 03010200
    kworker/0:1H-40    [000] ....    : bh_stats: IND/REQ/CNF:  0/  0/  1, REQ in progress:  0, WUP: release

... while the following is not:
    kworker/u2:1-24    [000] ....    : io_read32: CONTROL: 00003000
    kworker/u2:1-24    [000] ....    : io_read32: CONTROL: 00003000
    kworker/u2:1-24    [000] ....    : io_read32: CONTROL: 00003000
    [...loop until timeout...]
    wfx-sdio mmc0:0001:1: time out while polling control register

Signed-off-by: Jérôme Pouiller <jerome.pouiller@...abs.com>
---
 drivers/staging/wfx/bh.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/staging/wfx/bh.c b/drivers/staging/wfx/bh.c
index 4c6ba9c342a6..bcea9d5b119c 100644
--- a/drivers/staging/wfx/bh.c
+++ b/drivers/staging/wfx/bh.c
@@ -295,6 +295,7 @@ void wfx_bh_poll_irq(struct wfx_dev *wdev)
 	u32 reg;
 
 	WARN(!wdev->poll_irq, "unexpected IRQ polling can mask IRQ");
+	flush_workqueue(system_highpri_wq);
 	start = ktime_get();
 	for (;;) {
 		wfx_control_reg_read(wdev, &reg);
-- 
2.34.1