linux-kernel - Re: [PATCH 16/17] auxdisplay: ht16k33: Add support for segment displays

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Date:   Mon, 29 Mar 2021 09:08:59 +0200
From:   Robin van der Gracht <robin@...tonic.nl>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Rob Herring <robh+dt@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
        Paul Burton <paulburton@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devicetree@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/17] auxdisplay: ht16k33: Add support for segment
 displays

Hello Geert,

On 2021-03-22 15:48, Geert Uytterhoeven wrote:
> The Holtek HT16K33 LED controller is not only used for driving
> dot-matrix displays, but also for driving segment displays.
> 
> Add support for 4-digit 7-segment and quad 14-segment alphanumeric
> displays, like the Adafruit 7-segment and 14-segment display backpack
> and FeatherWing expansion boards.  Use the character line display core
> support to display a message, which will be scrolled if it doesn't fit.
> 
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
> The 7-segment support is based on schematics, and untested on actual
> hardware.
> ---
>  drivers/auxdisplay/ht16k33.c | 198 +++++++++++++++++++++++++++++++++--
>  1 file changed, 191 insertions(+), 7 deletions(-)
> 
...
> 
> +static int ht16k33_seg_probe(struct i2c_client *client,
> +			     struct ht16k33_priv *priv, uint32_t brightness)
> +{
> +	struct ht16k33_seg *seg = &priv->seg;
> +	struct device *dev = &client->dev;
> +	int err;
> +
> +	err = ht16k33_brightness_set(priv, MAX_BRIGHTNESS);
> +	if (err)
> +		return err;
> +
> +	switch (priv->type) {
> +	case DISP_MATRIX:
> +		/* not handled here */
> +		break;

This 'case' shouldn't happen. Having said that, the break here will 
still
cause the linedisp_register() function to be called for the DISP_MATRIX 
type.
If you'd like to handle this case, a return (or setting 'err') should
prevent this.

> +
> +	case DISP_QUAD_7SEG:
> +		INIT_DELAYED_WORK(&priv->work, ht16k33_seg7_update);
> +		seg->map.seg7 = initial_map_seg7;
> +		seg->map_size = sizeof(seg->map.seg7);
> +		err = device_create_file(dev, &dev_attr_map_seg7);
> +		break;
> +
> +	case DISP_QUAD_14SEG:
> +		INIT_DELAYED_WORK(&priv->work, ht16k33_seg14_update);
> +		seg->map.seg14 = initial_map_seg14;
> +		seg->map_size = sizeof(seg->map.seg14);
> +		err = device_create_file(dev, &dev_attr_map_seg14);
> +		break;
> +	}
> +	if (err)
> +		return err;
> +
> +	err = linedisp_register(&seg->linedisp, dev, 4, seg->curr,
> +				ht16k33_linedisp_update);
> +	if (err)
> +		goto err_remove_map_file;
> +
> +	return 0;

Groetjes/Kind regards,
Robin van der Gracht