[PATCH 2/6] mfd: Add ST Multi-Function eXpander core driver

On 02/22/2018 02:44 PM, Linus Walleij wrote:

On Thu, Feb 8, 2018 at 3:27 PM, Amelie Delaunay [off-list ref] wrote:

Thanks for working on this complex expander driver.
It is a bit daunting. Sorry if there are lots of comments and
considerations, but it reflects the complexity of the hardware.

quoted

+enum mfx_block {
+       MFX_BLOCK_GPIO          = BIT(0),
+       MFX_BLOCK_TS            = BIT(1),
+       MFX_BLOCK_IDD           = BIT(2),
+       MFX_BLOCK_ALTGPIO       = BIT(3),
+};

This looks suspiciously similar to this:

enum stmpe_block {
         STMPE_BLOCK_GPIO        = 1 << 0,
         STMPE_BLOCK_KEYPAD      = 1 << 1,
         STMPE_BLOCK_TOUCHSCREEN = 1 << 2,
         STMPE_BLOCK_ADC         = 1 << 3,
         STMPE_BLOCK_PWM         = 1 << 4,
         STMPE_BLOCK_ROTATOR     = 1 << 5,
};

Apparently the same hardware designers are involved.

Or the firmware developers were heavely inspired by STMPE!

quoted

+int mfx_reg_write(struct mfx *mfx, u8 reg, u8 data);
+int mfx_reg_read(struct mfx *mfx, u8 reg);
+int mfx_block_read(struct mfx *mfx, u8 reg, u8 length, u8 *values);
+int mfx_block_write(struct mfx *mfx, u8 reg, u8 length, const u8 *values);
+int mfx_set_bits(struct mfx *mfx, u8 reg, u8 mask, u8 val);

Do you need this? Can't you just use regmap and pass
around a struct regmap *map to access registers?

You don't necessarily need to use the default I2C regmap
(like, e.g. drivers/mfd/stw481x.c) but even if a more
complex access pattern is used to read/write registers
I am pretty sure you can use regmap for it.

Yes, Lee has also raised this point.

quoted

+int mfx_enable(struct mfx *mfx, unsigned int blocks);
+int mfx_disable(struct mfx *mfx, unsigned int blocks);

This is similar to
extern int stmpe_enable(struct stmpe *stmpe, unsigned int blocks);
extern int stmpe_disable(struct stmpe *stmpe, unsigned int blocks);

So again I am suspicious about duplication of driver code.

It even looks a bit like this driver started as a copy of
the STMPE driver, which is not a good sign. It might be
that it was copied from there because the hardware is
actually very similar.

HW is different, FW looks like similar.

quoted

+/* General */
+#define MFX_REG_CHIP_ID                        0x00 /* R */
+#define MFX_REG_FW_VERSION_MSB         0x01 /* R */
+#define MFX_REG_FW_VERSION_LSB         0x02 /* R */
+#define MFX_REG_SYS_CTRL               0x40 /* RW */

The STMPE driver defines enumerated registers in
include/linux/mfd/stmpe.h
then assign each variant using the model specifics in
drivers/mfd/stmpe.h

This doesn't seem super much different.

Even if the old STMPE driver may be a bad fit, is is better
to improve that (e.g. migrate it to use regmap and rewrite the
stmpe-gpio.c driver to use pin control) and use also for this
driver, or write a new driver from scratch like this?

I'm not so sure.

I do know that developers not always like to take out old
hardware and old development boards and start hacking
away before they can get some nice new hardware going
but I am worried that this may be one of those cases where
a serious cleanup of the aging STMPE driver may be a
first necessary step.

Just looking at [1], we see that the STMPE remaining active are the 
STMPE1600 and STMPE1801. All the others are obsolete.

[1] 
http://www.st.com/en/interfaces-and-transceivers/i-o-expanders.html?querycriteria=productId=SC1027

quoted

+/* IRQ output management */
+#define MFX_REG_IRQ_OUT_PIN            0x41 /* RW */
+#define MFX_REG_IRQ_SRC_EN             0x42 /* RW */
+#define MFX_REG_IRQ_PENDING            0x08 /* R */
+#define MFX_REG_IRQ_ACK                        0x44 /* RW */

Very similar to STMPE it seems.

IRQ_OUT_PIN is different (edge not supported, open drain or push pull 
output) and IRQ_ACK new.

quoted

+/* MFX_REG_SYS_CTRL bitfields */
+#define MFX_REG_SYS_CTRL_GPIO_EN       BIT(0)
+#define MFX_REG_SYS_CTRL_TS_EN         BIT(1)
+#define MFX_REG_SYS_CTRL_IDD_EN                BIT(2)
+#define MFX_REG_SYS_CTRL_ALTGPIO_EN    BIT(3)

I guess these blocks works the same as with STMPE,
that you can only use one of them at the time?

What is altgpio?

ALTGPIO enables the use of GPIO[23:16] only if IDD and/or TS is/are 
disabled. TS and IDD have priority, if IDD and TS are enabled, ALTGPIO 
is forced to 0 by MFX FW.
When IDD is used GPIO[19:16] can be used as GPIO.
When TS is used GPIO[24:20] can be used as GPIO.

quoted

+/* MFX_REG_IRQ_OUT_PIN bitfields */
+#define MFX_REG_IRQ_OUT_PIN_TYPE       BIT(0) /* 0-OD 1-PP */
+#define MFX_REG_IRQ_OUT_PIN_POL                BIT(1) /* 0-active LOW 1-active HIGH */

I have not read the patch yet. But just for notice:
This output IRQ type needs to be handled as well.

Check the code in
drivers/iio/common/st_sensors/st_sensors_trigger.c

To see how you can detect the properties of an IRQ
to set the right polarity, and handling of open drain
IRQ lines.

Thanks, I will have a look on this driver.
Regards,
Amelie

Yours,
Linus Walleij