From: Zev Weiss <zev@bewilderbeest.net>
To: Brendan Higgins <brendanhiggins@google.com>
Cc: Zev Weiss <zev@bewilderbeest.net>, Joel Stanley <joel@jms.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Andrew Jeffery <andrew@aj.id.au>,
linux-i2c@vger.kernel.org, openbmc@lists.ozlabs.org,
linux-arm-kernel@lists.infradead.org,
linux-aspeed@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2] i2c: aspeed: disable additional device addresses on ast2[56]xx
Date: Thu, 6 May 2021 15:54:19 -0500 [thread overview]
Message-ID: <20210506205419.26294-1-zev@bewilderbeest.net> (raw)
The ast25xx and ast26xx have, respectively, two and three configurable
slave device addresses to the ast24xx's one. We only support using
one at a time, but the others may come up in an indeterminate state
depending on hardware/bootloader behavior, so we need to make sure we
disable them so as to avoid ending up with phantom devices on the bus.
Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
---
Changes since v1 [0]:
- reduced to simplified approach suggested by Joel
[0] https://lore.kernel.org/linux-arm-kernel/20200915184525.29665-1-zev@bewilderbeest.net/
drivers/i2c/busses/i2c-aspeed.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index 724bf30600d6..67e8b97c0c95 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/drivers/i2c/busses/i2c-aspeed.c
@@ -727,10 +727,14 @@ static void __aspeed_i2c_reg_slave(struct aspeed_i2c_bus *bus, u16 slave_addr)
{
u32 addr_reg_val, func_ctrl_reg_val;
- /* Set slave addr. */
- addr_reg_val = readl(bus->base + ASPEED_I2C_DEV_ADDR_REG);
- addr_reg_val &= ~ASPEED_I2CD_DEV_ADDR_MASK;
- addr_reg_val |= slave_addr & ASPEED_I2CD_DEV_ADDR_MASK;
+ /*
+ * Set slave addr. Reserved bits can all safely be written with zeros
+ * on all of ast2[456]00, so zero everything else to ensure we only
+ * enable a single slave address (ast2500 has two, ast2600 has three,
+ * the enable bits for which are also in this register) so that we don't
+ * end up with additional phantom devices responding on the bus.
+ */
+ addr_reg_val = slave_addr & ASPEED_I2CD_DEV_ADDR_MASK;
writel(addr_reg_val, bus->base + ASPEED_I2C_DEV_ADDR_REG);
/* Turn on slave mode. */
--
2.31.1
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next reply other threads:[~2021-05-06 20:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-06 20:54 Zev Weiss [this message]
2021-05-07 19:57 ` [PATCH v2] i2c: aspeed: disable additional device addresses on ast2[56]xx Brendan Higgins
2021-05-21 2:43 ` Joel Stanley
2021-05-27 19:46 ` Wolfram Sang
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