Re: [PATCH 2/4] i2c: nomadik: support Mobileye EyeQ6H I2C controller

[Théo Lebrun]

Hello Krzysztof,

On Tue Oct 8, 2024 at 3:39 PM CEST, Krzysztof Kozlowski wrote:
> On Tue, Oct 08, 2024 at 12:29:41PM +0200, Théo Lebrun wrote:
> > Add EyeQ6H support to the nmk-i2c AMBA driver. It shares the same quirk
> > as EyeQ5: the memory bus only supports 32-bit accesses. Avoid writeb()
> > and readb() by reusing the same `priv->has_32b_bus` flag.
> > 
> > It does NOT need to write speed-mode specific value into a register;
> > therefore it does not depend on the mobileye,olb DT property.
> > 
> > Refactoring is done using is_eyeq5 and is_eyeq6h boolean local
> > variables. Sort variables in reverse christmas tree to try and
> > introduce some logic into the ordering.
> > 
> > Signed-off-by: Théo Lebrun <theo.lebrun@xxxxxxxxxxx>
> > ---
> >  drivers/i2c/busses/i2c-nomadik.c | 22 +++++++++++-----------
> >  1 file changed, 11 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-nomadik.c b/drivers/i2c/busses/i2c-nomadik.c
> > index ad0f02acdb1215a1c04729f97bb14a4d93f88456..ea511d3a58073eaedb63850026e05b59427a69c6 100644
> > --- a/drivers/i2c/busses/i2c-nomadik.c
> > +++ b/drivers/i2c/busses/i2c-nomadik.c
> > @@ -6,10 +6,10 @@
> >   * I2C master mode controller driver, used in Nomadik 8815
> >   * and Ux500 platforms.
> >   *
> > - * The Mobileye EyeQ5 platform is also supported; it uses
> > + * The Mobileye EyeQ5 and EyeQ6H platforms are also supported; they use
> >   * the same Ux500/DB8500 IP block with two quirks:
> >   *  - The memory bus only supports 32-bit accesses.
> > - *  - A register must be configured for the I2C speed mode;
> > + *  - (only EyeQ5) A register must be configured for the I2C speed mode;
> >   *    it is located in a shared register region called OLB.
> >   *
> >   * Author: Srinidhi Kasagar <srinidhi.kasagar@xxxxxxxxxxxxxx>
> > @@ -1046,8 +1046,6 @@ static int nmk_i2c_eyeq5_probe(struct nmk_i2c_dev *priv)
> >  	struct regmap *olb;
> >  	unsigned int id;
> >  
> > -	priv->has_32b_bus = true;
> > -
> >  	olb = syscon_regmap_lookup_by_phandle_args(np, "mobileye,olb", 1, &id);
> >  	if (IS_ERR(olb))
> >  		return PTR_ERR(olb);
> > @@ -1070,13 +1068,15 @@ static int nmk_i2c_eyeq5_probe(struct nmk_i2c_dev *priv)
> >  
> >  static int nmk_i2c_probe(struct amba_device *adev, const struct amba_id *id)
> >  {
> > -	int ret = 0;
> > -	struct nmk_i2c_dev *priv;
> > -	struct device_node *np = adev->dev.of_node;
> > -	struct device *dev = &adev->dev;
> > -	struct i2c_adapter *adap;
> >  	struct i2c_vendor_data *vendor = id->data;
> > +	struct device_node *np = adev->dev.of_node;
> > +	bool is_eyeq6h = of_device_is_compatible(np, "mobileye,eyeq6h-i2c");
> > +	bool is_eyeq5 = of_device_is_compatible(np, "mobileye,eyeq5-i2c");
>
> You should use match data, not add compatibles in the middle of code.
> That's preferred, scallable pattern. What you added here last time does
> not scale and above change is a proof for that.

I would have used match data if the driver struct had a .of_match_table
field. `struct amba_driver` does not. Are you recommending the approach
below?

I don't see how it brings much to the driver but I do get the scaling
issue as the number of support compatibles increases. This is a fear
based on what *could* happen in the future though.

------------------------------------------------------------------------

diff --git a/drivers/i2c/busses/i2c-nomadik.c b/drivers/i2c/busses/i2c-nomadik.c
index 82571983bbca..98fc40dfcbfc 100644
--- a/drivers/i2c/busses/i2c-nomadik.c
+++ b/drivers/i2c/busses/i2c-nomadik.c
@@ -26,6 +26,7 @@
 #include <linux/mfd/syscon.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_device.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/pm_runtime.h>
 #include <linux/regmap.h>
@@ -1061,28 +1062,46 @@ static int nmk_i2c_eyeq5_probe(struct nmk_i2c_dev *priv)
 	return 0;
 }

+#define NMK_I2C_EYEQ_FLAG_32B_BUS	BIT(0)
+#define NMK_I2C_EYEQ_FLAG_IS_EYEQ5	BIT(1)
+
+static const struct of_device_id nmk_i2c_eyeq_match_table[] = {
+	{
+		.compatible = "mobileye,eyeq5-i2c",
+		.data = (void*)(NMK_I2C_EYEQ_FLAG_32B_BUS | NMK_I2C_EYEQ_FLAG_IS_EYEQ5),
+	},
+	{
+		.compatible = "mobileye,eyeq6h-i2c",
+		.data = (void*)(NMK_I2C_EYEQ_FLAG_32B_BUS),
+	},
+};
+
 static int nmk_i2c_probe(struct amba_device *adev, const struct amba_id *id)
 {
 	struct i2c_vendor_data *vendor = id->data;
 	struct device_node *np = adev->dev.of_node;
-	bool is_eyeq6h = of_device_is_compatible(np, "mobileye,eyeq6h-i2c");
-	bool is_eyeq5 = of_device_is_compatible(np, "mobileye,eyeq5-i2c");
 	u32 max_fifo_threshold = (vendor->fifodepth / 2) - 1;
+	const struct of_device_id *match;
 	struct device *dev = &adev->dev;
+	unsigned long match_flags = 0;
 	struct nmk_i2c_dev *priv;
 	struct i2c_adapter *adap;
 	int ret = 0;

+	match = of_match_device(nmk_i2c_eyeq_match_table, dev);
+	if (match)
+		match_flags = (unsigned long)match->data;
+
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;

 	priv->vendor = vendor;
 	priv->adev = adev;
-	priv->has_32b_bus = is_eyeq5 || is_eyeq6h;
+	priv->has_32b_bus = match_flags & NMK_I2C_EYEQ_FLAG_32B_BUS;
 	nmk_i2c_of_probe(np, priv);

-	if (is_eyeq5) {
+	if (match_flags & NMK_I2C_EYEQ_FLAG_IS_EYEQ5) {
 		ret = nmk_i2c_eyeq5_probe(priv);
 		if (ret)
 			return dev_err_probe(dev, ret, "failed OLB lookup\n");

------------------------------------------------------------------------

Thanks Krzysztof,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com