linux-kernel - Re: [PATCH v4 3/6] drm: Add driver for Solomon SSD130x OLED displays

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Date:   Fri, 11 Feb 2022 13:33:58 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Maxime Ripard <maxime@...no.tech>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Sam Ravnborg <sam@...nborg.org>,
        Noralf Trønnes <noralf@...nnes.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Lee Jones <lee.jones@...aro.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v4 3/6] drm: Add driver for Solomon SSD130x OLED displays

On Fri, Feb 11, 2022 at 10:19:24AM +0100, Javier Martinez Canillas wrote:
> This adds a DRM driver for SSD1305, SSD1306, SSD1307 and SSD1309 Solomon
> OLED display controllers.
> 
> It's only the core part of the driver and a bus specific driver is needed
> for each transport interface supported by the display controllers.

...

> +#include <linux/backlight.h>
> +#include <linux/bitfield.h>

bits.h
(FYI, specifically sent a patch few days ago to add explicitly the inclusions
 that needed for bitfield operations in the example inside bitfield.h).

> +#include <linux/delay.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/property.h>
> +#include <linux/pwm.h>
> +#include <linux/regulator/consumer.h>

...

> +#define SSD130X_SET_ADDRESS_MODE_HORIZONTAL	(0x00)
> +#define SSD130X_SET_ADDRESS_MODE_VERTICAL	(0x01)
> +#define SSD130X_SET_ADDRESS_MODE_PAGE		(0x02)
> +
> +#define SSD130X_SET_AREA_COLOR_MODE_ENABLE	(0x1e)
> +#define SSD130X_SET_AREA_COLOR_MODE_LOW_POWER	(0x05)

Do the parentheses add anything here?

...

> +/*
> + * Helper to write command (SSD130X_COMMAND). The fist variadic argument
> + * is the command to write and the following are the command options.

This is not correct explanation. Please, rephrase to show that _each_ of the
options is sent with a preceding command.

> + */
> +static int ssd130x_write_cmd(struct ssd130x_device *ssd130x, int count,
> +				    /* u8 cmd, u8 option, ... */...)
> +{
> +	va_list ap;
> +	u8 value;
> +	int ret;
> +
> +	va_start(ap, count);
> +
> +	do {
> +		value = va_arg(ap, int);
> +		ret = regmap_write(ssd130x->regmap, SSD130X_COMMAND, (u8)value);
> +		if (ret)
> +			goto out_end;
> +	} while (--count);
> +
> +out_end:
> +	va_end(ap);
> +
> +	return ret;
> +}

...

> +	if (ssd130x->device_info->need_pwm) {

Yeah, unfortunately we still don't have pwm_get_optional()...

> +		ret = ssd130x_pwm_enable(ssd130x);
> +		if (ret) {
> +			dev_err(dev, "Failed to enable PWM: %d\n", ret);
> +			regulator_disable(ssd130x->vcc_reg);
> +			return ret;
> +		}
> +	}

...

> +static void ssd130x_power_off(struct ssd130x_device *ssd130x)
> +{

> +	if (ssd130x->device_info->need_pwm) {

Redundant check. The two below are NULL-aware.

> +		pwm_disable(ssd130x->pwm);
> +		pwm_put(ssd130x->pwm);
> +	}
> +
> +	regulator_disable(ssd130x->vcc_reg);
> +}

...

> +	ret = ssd130x_write_cmd(ssd130x, 2, SSD130X_SET_COM_PINS_CONFIG, compins);
> +	if (ret < 0)
> +		return ret;

> +
> +

One blank line is enough.

...

> +	for (i = y / 8; i < y / 8 + pages; i++) {
> +		int m = 8;
> +
> +		/* Last page may be partial */
> +		if (8 * (i + 1) > ssd130x->height)
> +			m = ssd130x->height % 8;

Perhaps it can be moved out of the loop with refactored piece below.

> +		for (j = x; j < x + width; j++) {
> +			u8 data = 0;
> +
> +			for (k = 0; k < m; k++) {
> +				u8 byte = buf[(8 * i + k) * line_length + j / 8];
> +				u8 bit = (byte >> (j % 8)) & 1;
> +
> +				data |= bit << k;
> +			}
> +			data_array[array_idx++] = data;
> +		}
> +	}

...

> +	bl = devm_backlight_device_register(dev, dev_name(dev), dev, ssd130x,
> +					    &ssd130xfb_bl_ops, NULL);
> +	if (IS_ERR(bl)) {

> +		ret = PTR_ERR(bl);
> +		dev_err_probe(dev, ret, "Unable to register backlight device\n");
> +		return ERR_PTR(ret);

		dev_err_probe(dev, PTR_ERR(bl), "Unable to register backlight device\n");
		return bl;

?

> +	}

-- 
With Best Regards,
Andy Shevchenko