linux-kernel - Re: [PATCH v3 2/5] gpio: gxp: Add HPE GXP GPIO

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Date:   Wed, 7 Jun 2023 20:45:26 +0000
From:   "Hawkins, Nick" <nick.hawkins@....com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     "Verdun, Jean-Marie" <verdun@....com>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "brgl@...ev.pl" <brgl@...ev.pl>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>
Subject: Re: [PATCH v3 2/5] gpio: gxp: Add HPE GXP GPIO

> It does care about things the average GPIO controller driver needs to
> repeat. So at least you may try and see how it will look.


> > If gpio_regmap is required, how do I create a direct correlation
> > between a specific gpio-line and a register offset? For example, in
> > gpio-gxp-pl.c. Gpio-line at offset 0 (IOPLED) is at register 0x04. The
> > gpio-line at offset 8 (FAN_INST) is at register 0x27.


> You may remap registers. See, for example, gpio-pca953x, where some of
> the registers (with high bit set) are actually virtual rather than
> real offsets. Similar idea can be used in your case.

Greetings Andy,

Is there any documents available describing how regmap_gpio
populates the GPIO lines? Does it automatically go through and add lines
for each successful regmap_read and bits per byte?

I have taken your advice and used the additional readable and writeable
on regmap_config to limit the number of accessible registers.

static const struct regmap_config gxp_regmap_config = {
        .reg_bits = 8,
        .reg_stride = 1,
        .val_bits = 8,
        .readable_reg = gxp_readable_register,
        .writeable_reg = gxp_writeable_register,
        .max_register = 0x80,
        .name = "gxp-gpio-pl",
};

static const struct regmap_config gxp_int_regmap_config = {
        .reg_bits = 8,
        .reg_stride = 1,
        .val_bits = 8,
        .readable_reg = gxp_read_write_int_register,
        .writeable_reg = gxp_read_write_int_register,
        .max_register = 0x7f
        .name = "gxp-gpio-pl-int"
};

Thanks,

-Nick Hawkins