[PATCH 5.18 068/231] net: ocelot: fix wrong time_after usage

Greg Kroah-Hartman
2022-07-19T12:55:19Z

From: Pavel Skripkin <paskripkin@gmail.com>

[ Upstream commit f46fd3d7c3bd5d7bd5bb664135cf32ca9e97190b ]

Accidentally noticed, that this driver is the only user of
while (time_after(jiffies...)).

It looks like typo, because likely this while loop will finish after 1st
iteration, because time_after() returns true when 1st argument _is after_
2nd one.

There is one possible problem with this poll loop: the scheduler could put
the thread to sleep, and it does not get woken up for
OCELOT_FDMA_CH_SAFE_TIMEOUT_US. During that time, the hardware has done
its thing, but you exit the while loop and return -ETIMEDOUT.

Fix it by using sane poll API that avoids all problems described above

Fixes: 753a026cfec1 ("net: ocelot: add FDMA support")
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20220706132845.27968-1-paskripkin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/mscc/ocelot_fdma.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot_fdma.c b/drivers/net/ethernet/mscc/ocelot_fdma.c
index dffa597bffe6..6a8f84f325a3 100644
--- a/drivers/net/ethernet/mscc/ocelot_fdma.c
+++ b/drivers/net/ethernet/mscc/ocelot_fdma.c
@@ -94,19 +94,18 @@ static void ocelot_fdma_activate_chan(struct ocelot *ocelot, dma_addr_t dma,
ocelot_fdma_writel(ocelot, MSCC_FDMA_CH_ACTIVATE, BIT(chan));
}

+static u32 ocelot_fdma_read_ch_safe(struct ocelot *ocelot)
+{
+ return ocelot_fdma_readl(ocelot, MSCC_FDMA_CH_SAFE);
+}
+
static int ocelot_fdma_wait_chan_safe(struct ocelot *ocelot, int chan)
{
- unsigned long timeout;
u32 safe;

- timeout = jiffies + usecs_to_jiffies(OCELOT_FDMA_CH_SAFE_TIMEOUT_US);
- do {
- safe = ocelot_fdma_readl(ocelot, MSCC_FDMA_CH_SAFE);
- if (safe & BIT(chan))
- return 0;
- } while (time_after(jiffies, timeout));
-
- return -ETIMEDOUT;
+ return readx_poll_timeout_atomic(ocelot_fdma_read_ch_safe, ocelot, safe,
+ safe & BIT(chan), 0,
+ OCELOT_FDMA_CH_SAFE_TIMEOUT_US);
}

static void ocelot_fdma_dcb_set_data(struct ocelot_fdma_dcb *dcb,
--
2.35.1