Re: [PATCH v2 2/2] drm/tiny: Add driver for Sharp Memory LCD

[Alex Lanzano]

On Sat, Jul 27, 2024 at 12:12:01AM GMT, Christophe JAILLET wrote:
> Le 26/07/2024 à 21:44, Alex Lanzano a écrit :
> > Add support for the monochrome Sharp Memory LCDs.
> > 
> > Signed-off-by: Alex Lanzano <lanzano.alex-Re5JQEeQqe8AvxtiuMwx3w@xxxxxxxxxxxxxxxx>
> > Co-developed-by: Mehdi Djait <mehdi.djait-LDxbnhwyfcJBDgjK7y7TUQ@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Mehdi Djait <mehdi.djait-LDxbnhwyfcJBDgjK7y7TUQ@xxxxxxxxxxxxxxxx>
> > ---
> >   MAINTAINERS                         |   7 +
> >   drivers/gpu/drm/tiny/Kconfig        |  20 +
> >   drivers/gpu/drm/tiny/Makefile       |   1 +
> >   drivers/gpu/drm/tiny/sharp-memory.c | 726 ++++++++++++++++++++++++++++
> >   4 files changed, 754 insertions(+)
> >   create mode 100644 drivers/gpu/drm/tiny/sharp-memory.c
> > 
> 
> Hi,
> 
> below some other tiny comments, hoping it helps.
> 
> Also "./scripts/checkpatch.pl --strict" gives some hints, should some be of
> interest.
> 

Ah! Thank you. I'll be sure to use strict from now on

> > +static int sharp_memory_probe(struct spi_device *spi)
> > +{
> > +	int ret;
> > +	struct device *dev;
> > +	struct sharp_memory_device *smd;
> > +	enum sharp_memory_model model;
> > +	struct drm_device *drm;
> > +	const char *vcom_mode_str;
> > +
> > +	ret = spi_setup(spi);
> > +	if (ret < 0)
> > +		return dev_err_probe(&spi->dev, ret, "Failed to setup spi device\n");
> > +
> > +	dev = &spi->dev;
> 
> 6 times below, &spi->dev could be replaced by dev, to slightly simplify
> things.
> 
> > +	if (!dev->coherent_dma_mask) {
> > +		ret = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(32));
> > +		if (ret)
> > +			return dev_err_probe(dev, ret, "Failed to set dma mask\n");
> > +	}
> > +
> > +	smd = devm_drm_dev_alloc(&spi->dev, &sharp_memory_drm_driver,
> > +				 struct sharp_memory_device, drm);
> 
> Missing error handling.
> 
> > +
> > +	spi_set_drvdata(spi, smd);
> > +
> > +	smd->spi = spi;
> > +	drm = &smd->drm;
> > +	ret = drmm_mode_config_init(drm);
> > +	if (ret)
> > +		return dev_err_probe(dev, ret, "Failed to initialize drm config\n");
> > +
> > +	smd->enable_gpio = devm_gpiod_get_optional(dev, "enable", GPIOD_OUT_HIGH);
> > +	if (smd->enable_gpio == NULL)
> 
> Nitpick: if (!smd->enable_gpio)
> 
> > +		dev_warn(&spi->dev, "Enable gpio not defined\n");
> > +
> > +	/*
> > +	 * VCOM is a signal that prevents DC bias from being built up in
> > +	 * the panel resulting in pixels being forever stuck in one state.
> > +	 *
> > +	 * This driver supports three different methods to generate this
> > +	 * signal depending on EXTMODE pin:
> > +	 *
> > +	 * software (EXTMODE = L) - This mode uses a kthread to
> > +	 * periodically send a "maintain display" message to the display,
> > +	 * toggling the vcom bit on and off with each message
> > +	 *
> > +	 * external (EXTMODE = H) - This mode relies on an external
> > +	 * clock to generate the signal on the EXTCOMM pin
> > +	 *
> > +	 * pwm (EXTMODE = H) - This mode uses a pwm device to generate
> > +	 * the signal on the EXTCOMM pin
> > +	 *
> > +	 */
> > +	smd->vcom = 0;
> 
> Nitpick: devm_drm_dev_alloc() already zeroes the allocated memory. So this
> is useless. Unless you think it gives some useful hint, it could be removed.
> 
> > +	if (device_property_read_string(&spi->dev, "vcom-mode", &vcom_mode_str))
> > +		return dev_err_probe(dev, -EINVAL,
> > +				     "Unable to find vcom-mode node in device tree\n");
> > +
> > +	if (!strcmp("software", vcom_mode_str)) {
> > +		smd->vcom_mode = SHARP_MEMORY_SOFTWARE_VCOM;
> 
> ...
> 
> > +	smd->pitch = (SHARP_ADDR_PERIOD + smd->mode->hdisplay + SHARP_DUMMY_PERIOD) / 8;
> > +	smd->tx_buffer_size = (SHARP_MODE_PERIOD +
> > +			       (SHARP_ADDR_PERIOD + (smd->mode->hdisplay) + SHARP_DUMMY_PERIOD) *
> > +			       smd->mode->vdisplay) / 8;
> > +
> > +	smd->tx_buffer = devm_kzalloc(&spi->dev, smd->tx_buffer_size, GFP_KERNEL);
> > +	if (!smd->tx_buffer)
> > +		return dev_err_probe(&spi->dev, -ENOMEM, "Unable to alloc tx buffer\n");
> 
> There is no need to log a message for memory allocation failure.
> return -ENOMEM; should be just fine IMHO.
> 
> > +
> > +	mutex_init(&smd->tx_mutex);
> > +
> > +	drm->mode_config.min_width = smd->mode->hdisplay;
> > +	drm->mode_config.max_width = smd->mode->hdisplay;
> > +	drm->mode_config.min_height = smd->mode->vdisplay;
> > +	drm->mode_config.max_height = smd->mode->vdisplay;
> > +
> > +	ret = sharp_memory_pipe_init(drm, smd,
> > +				     sharp_memory_formats,
> 
> Nitpick: you could save 1 LoC if this is put at the end of the previous
> line.
> 
> > +				     ARRAY_SIZE(sharp_memory_formats),
> > +				     NULL);
> > +	if (ret)
> > +		return dev_err_probe(dev, ret, "Failed to initialize display pipeline.\n");
> > +
> > +	drm_plane_enable_fb_damage_clips(&smd->plane);
> > +	drm_mode_config_reset(drm);
> > +
> > +	ret = drm_dev_register(drm, 0);
> > +	if (ret)
> > +		return dev_err_probe(dev, ret, "Failed to register drm device.\n");
> > +
> > +	drm_fbdev_dma_setup(drm, 0);
> > +
> > +	return 0;
> > +}
> 
> ...
> 
> CJ
> 
> 

I appreciate the review! I'll get these addressed in v3

Best regards,
Alex