linux-kernel - Re: [PATCH v5 2/2] drm: bridge: Add support for Solomon SSD2825 RGB/DSI bridge

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Message-ID: <48472736-4182-4d47-9980-6d63541f6975@wanadoo.fr>
Date: Tue, 6 May 2025 19:49:44 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: clamor95@...il.com
Cc: Laurent.pinchart@...asonboard.com, airlied@...il.com,
 andrzej.hajda@...el.com, conor+dt@...nel.org, devicetree@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, jernej.skrabec@...il.com, jonas@...boo.se,
 krzk+dt@...nel.org, linux-kernel@...r.kernel.org,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
 neil.armstrong@...aro.org, rfoss@...nel.org, robh@...nel.org,
 simona@...ll.ch, tzimmermann@...e.de
Subject: Re: [PATCH v5 2/2] drm: bridge: Add support for Solomon SSD2825
 RGB/DSI bridge

Le 06/05/2025 à 11:33, Svyatoslav Ryhel a écrit :
> SSD2825 is a cost-effective MIPI Bridge Chip solution targeting mainly
> smartphones. It can convert 24bit RGB interface into 4-lane MIPI-DSI
> interface to drive display modules of up to 800 x 1366, while supporting
> AMOLED, a-si LCD or LTPS panel technologies for smartphone applications.

Hi,

...

> +config DRM_SOLOMON_SSD2825
> +	tristate "SSD2825 RGB/DSI bridge"
> +	depends on SPI_MASTER && OF
> +	select DRM_MIPI_DSI
> +	select DRM_KMS_HELPER
> +	select DRM_PANEL
> +	help
> +	  Say Y here if you want support for the Solomon SSD2825 RGB/DSI
> +	  SPI bridge driver.
> +
> +	  Say M here if you want to support this hardware as a module.
> +	  The module will be named "solomon-ssd2825".

Is it "solomon-ssd2825" or just "ssd2825"?

> +
>   config DRM_THINE_THC63LVD1024
>   	tristate "Thine THC63LVD1024 LVDS decoder bridge"
>   	depends on OF

...

> +static int ssd2825_read_raw(struct ssd2825_priv *priv, u8 cmd, u16 *data)
> +{
> +	struct spi_device *spi = priv->spi;
> +	struct spi_message msg;
> +	struct spi_transfer xfer[2];
> +	u8 tx_buf[2];
> +	u8 rx_buf[2];
> +	int ret;
> +
> +	memset(&xfer, 0, sizeof(xfer));
> +
> +	tx_buf[1] = (cmd & 0xFF00) >> 8;
> +	tx_buf[0] = (cmd & 0x00FF);
> +
> +	xfer[0].tx_buf = tx_buf;
> +	xfer[0].bits_per_word = 9;
> +	xfer[0].len = 2;
> +
> +	xfer[1].rx_buf = rx_buf;
> +	xfer[1].bits_per_word = 16;
> +	xfer[1].len = 2;
> +
> +	spi_message_init(&msg);
> +	spi_message_add_tail(&xfer[0], &msg);
> +	spi_message_add_tail(&xfer[1], &msg);
> +
> +	ret = spi_sync(spi, &msg);
> +	if (ret)
> +		dev_err(&spi->dev, "spi_sync_read failed %d\n", ret);

Maybe, just spi_sync in the message?

> +
> +	*data = rx_buf[1] | (rx_buf[0] << 8);
> +
> +	return 0;

Is it on purpose that ret is never returned?
Is it safe to update *data if ret is not 0?

> +}

...

CJ