linux-kernel - Re: [PATCH 1/3] i2c: aspeed: avoid new registers definition of AST2600

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Date:   Wed, 19 May 2021 19:02:50 +0000
From:   Zev Weiss <zweiss@...inix.com>
To:     Jamin Lin <jamin_lin@...eedtech.com>
CC:     Rob Herring <robh+dt@...nel.org>, Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "open list:I2C SUBSYSTEM HOST DRIVERS" <linux-i2c@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/ASPEED MACHINE SUPPORT" 
        <linux-aspeed@...ts.ozlabs.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/ASPEED I2C DRIVER" <openbmc@...ts.ozlabs.org>,
        "steven_lee@...eedtech.com" <steven_lee@...eedtech.com>,
        "chiawei_wang@...eedtech.com" <chiawei_wang@...eedtech.com>,
        "troy_lee@...eedtech.com" <troy_lee@...eedtech.com>,
        "ryan_chen@...eedtech.com" <ryan_chen@...eedtech.com>
Subject: Re: [PATCH 1/3] i2c: aspeed: avoid new registers definition of
 AST2600

On Wed, May 19, 2021 at 03:04:27AM CDT, Jamin Lin wrote:
>The register definition between AST2600 A2 and A3 is different.
>This patch avoid new registers definition of AST2600 to use
>this driver. We will submit the path for the new registers
>definition of AST2600.
>
>Signed-off-by: Jamin Lin <jamin_lin@...eedtech.com>
>---
> drivers/i2c/busses/i2c-aspeed.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
>diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
>index 724bf30600d6..007309077d9f 100644
>--- a/drivers/i2c/busses/i2c-aspeed.c
>+++ b/drivers/i2c/busses/i2c-aspeed.c
>@@ -19,14 +19,20 @@
> #include <linux/irqchip/chained_irq.h>
> #include <linux/irqdomain.h>
> #include <linux/kernel.h>
>+#include <linux/mfd/syscon.h>
> #include <linux/module.h>
> #include <linux/of_address.h>
> #include <linux/of_irq.h>
> #include <linux/of_platform.h>
> #include <linux/platform_device.h>
>+#include <linux/regmap.h>
> #include <linux/reset.h>
> #include <linux/slab.h>
>
>+/* I2C Global Registers */
>+/* 0x0c : I2CG Global Control Register (AST2500)  */
>+#define ASPEED_I2CG_GLOBAL_CTRL_REG			0x0c
>+
> /* I2C Register */
> #define ASPEED_I2C_FUN_CTRL_REG				0x00
> #define ASPEED_I2C_AC_TIMING_REG1			0x04
>@@ -973,6 +979,22 @@ static int aspeed_i2c_probe_bus(struct platform_device *pdev)
> 	struct resource *res;
> 	int irq, ret;
>
>+	if (of_device_is_compatible(pdev->dev.of_node,
>+				    "aspeed,ast2600-i2c-bus")) {
>+		u32 global_ctrl;
>+		struct regmap *gr_regmap;
>+
>+		gr_regmap = syscon_regmap_lookup_by_compatible("aspeed,ast2600-i2c-global");
>+
>+		if (IS_ERR(gr_regmap)) {
>+			ret = PTR_ERR(gr_regmap);
>+		} else {
>+			regmap_read(gr_regmap, ASPEED_I2CG_GLOBAL_CTRL_REG, &global_ctrl);
>+			if (global_ctrl & BIT(2))
>+				return -EIO;

A macro definition might be a bit nicer than a raw BIT(2) here I'd
think.

Also, it seems a bit unfortunate to just bail on the device entirely if
we find this bit set (seems like a good way for a bootloader to
inadvertently DoS the kernel), though I guess poking global syscon bits
in the bus probe function might not be ideal.  Could/should we consider
some module-level init code to ensure that bit is cleared?


Zev

>+		}
>+	}
>+
> 	bus = devm_kzalloc(&pdev->dev, sizeof(*bus), GFP_KERNEL);
> 	if (!bus)
> 		return -ENOMEM;
>-- 
>2.17.1
>