[SRU][F][PATCH 1/1] serial: sc16is7xx: convert from _raw_ to _noinc_ regmap functions for FIFO

[Jacob Martin]

From: Hugo Villeneuve <hvilleneuve at dimonoff.com>

commit dbf4ab821804df071c8b566d9813083125e6d97b upstream.

The SC16IS7XX IC supports a burst mode to access the FIFOs where the
initial register address is sent ($00), followed by all the FIFO data
without having to resend the register address each time. In this mode, the
IC doesn't increment the register address for each R/W byte.

The regmap_raw_read() and regmap_raw_write() are functions which can
perform IO over multiple registers. They are currently used to read/write
from/to the FIFO, and although they operate correctly in this burst mode on
the SPI bus, they would corrupt the regmap cache if it was not disabled
manually. The reason is that when the R/W size is more than 1 byte, these
functions assume that the register address is incremented and handle the
cache accordingly.

Convert FIFO R/W functions to use the regmap _noinc_ versions in order to
remove the manual cache control which was a workaround when using the
_raw_ versions. FIFO registers are properly declared as volatile so
cache will not be used/updated for FIFO accesses.

Fixes: dfeae619d781 ("serial: sc16is7xx")
Cc:  <stable at vger.kernel.org>
Signed-off-by: Hugo Villeneuve <hvilleneuve at dimonoff.com>
Link: https://lore.kernel.org/r/20231211171353.2901416-6-hugo@hugovil.com
Cc: Hugo Villeneuve <hvilleneuve at dimonoff.com>
Signed-off-by: GONG, Ruiqi <gongruiqi1 at huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(backported from commit 4e37416e4ee1b1bc17364a68973e0c63be89e611 linux-5.10.y)
[jacobmartin: context adjustments for K5.4]
CVE-2023-52488
Signed-off-by: Jacob Martin <jacob.martin at canonical.com>
---
 drivers/tty/serial/sc16is7xx.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 8fb47f73cc7ad..01071e8ecfa78 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -376,9 +376,7 @@ static void sc16is7xx_fifo_read(struct uart_port *port, unsigned int rxlen)
 	const u8 line = sc16is7xx_line(port);
 	u8 addr = (SC16IS7XX_RHR_REG << SC16IS7XX_REG_SHIFT) | line;
 
-	regcache_cache_bypass(s->regmap, true);
-	regmap_raw_read(s->regmap, addr, s->buf, rxlen);
-	regcache_cache_bypass(s->regmap, false);
+	regmap_noinc_read(s->regmap, addr, s->buf, rxlen);
 }
 
 static void sc16is7xx_fifo_write(struct uart_port *port, u8 to_send)
@@ -394,9 +392,7 @@ static void sc16is7xx_fifo_write(struct uart_port *port, u8 to_send)
 	if (unlikely(!to_send))
 		return;
 
-	regcache_cache_bypass(s->regmap, true);
-	regmap_raw_write(s->regmap, addr, s->buf, to_send);
-	regcache_cache_bypass(s->regmap, false);
+	regmap_noinc_write(s->regmap, addr, s->buf, to_send);
 }
 
 static void sc16is7xx_port_update(struct uart_port *port, u8 reg,
@@ -489,6 +485,11 @@ static bool sc16is7xx_regmap_precious(struct device *dev, unsigned int reg)
 	return false;
 }
 
+static bool sc16is7xx_regmap_noinc(struct device *dev, unsigned int reg)
+{
+	return reg == SC16IS7XX_RHR_REG;
+}
+
 /*
  * Configure programmable baud rate generator (divisor) according to the
  * desired baud rate.
@@ -1414,6 +1415,8 @@ static struct regmap_config regcfg = {
 	.cache_type = REGCACHE_RBTREE,
 	.volatile_reg = sc16is7xx_regmap_volatile,
 	.precious_reg = sc16is7xx_regmap_precious,
+	.writeable_noinc_reg = sc16is7xx_regmap_noinc,
+	.readable_noinc_reg = sc16is7xx_regmap_noinc,
 };
 
 #ifdef CONFIG_SERIAL_SC16IS7XX_SPI
-- 
2.43.0