linux-kernel - Re: [PATCH 1/3] fbtft: Make sysfs and dev_*() logging conditional on FB

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Message-ID: <329423e8-d778-4f30-904a-825b1be72ce2@suse.de>
Date: Tue, 9 Dec 2025 08:25:39 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Chintan Patel <chintanlike@...il.com>, linux-fbdev@...r.kernel.org,
 linux-staging@...ts.linux.dev, linux-omap@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 andy@...nel.org, deller@....de, gregkh@...uxfoundation.org
Subject: Re: [PATCH 1/3] fbtft: Make sysfs and dev_*() logging conditional on
 FB_DEVICE

Hi

Am 09.12.25 um 05:27 schrieb Chintan Patel:
> The fbtft core and sysfs implementation unconditionally dereference
> fb_info->dev and register sysfs attributes. When FB_DEVICE=n, these
> fields are unavailable, leading to build failures.
>
> This patch wraps all sysfs attribute creation/removal and dev_dbg/dev_info
> logging in #ifdef CONFIG_FB_DEVICE, with pr_*() fallbacks for the
> non-FB_DEVICE case. This makes fbtft fully buildable when FB_DEVICE is
> disabled.
>
> Signed-off-by: Chintan Patel <chintanlike@...il.com>
> ---
>   drivers/staging/fbtft/fbtft-core.c  | 20 ++++++++++++++++++--
>   drivers/staging/fbtft/fbtft-sysfs.c |  8 ++++++++
>   2 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
> index 9e7b84071174..dc967bdeabe8 100644
> --- a/drivers/staging/fbtft/fbtft-core.c
> +++ b/drivers/staging/fbtft/fbtft-core.c
> @@ -365,9 +365,14 @@ static int fbtft_fb_setcolreg(unsigned int regno, unsigned int red,
>   	unsigned int val;
>   	int ret = 1;
>   
> +#ifdef CONFIG_FB_DEVICE
>   	dev_dbg(info->dev,

Rather use fb_dbg() [1] and similar helpers for logging. They only need 
the info pointer and do the correct output by themselves.

[1] https://elixir.bootlin.com/linux/v6.18/source/include/linux/fb.h#L895

>   		"%s(regno=%u, red=0x%X, green=0x%X, blue=0x%X, trans=0x%X)\n",
>   		__func__, regno, red, green, blue, transp);
> +#else
> +	pr_debug("%s(regno=%u, red=0x%X, green=0x%X, blue=0x%X, trans=0x%X)\n",
> +		 __func__, regno, red, green, blue, transp);
> +#endif
>   
>   	switch (info->fix.visual) {
>   	case FB_VISUAL_TRUECOLOR:
> @@ -391,8 +396,11 @@ static int fbtft_fb_blank(int blank, struct fb_info *info)
>   	struct fbtft_par *par = info->par;
>   	int ret = -EINVAL;
>   
> -	dev_dbg(info->dev, "%s(blank=%d)\n",
> -		__func__, blank);
> +#ifdef CONFIG_FB_DEVICE
> +	dev_dbg(info->dev, "%s(blank=%d)\n", __func__, blank);
> +#else
> +	pr_debug("%s(blank=%d)\n", __func__, blank);
> +#endif
>   
>   	if (!par->fbtftops.blank)
>   		return ret;
> @@ -793,6 +801,8 @@ int fbtft_register_framebuffer(struct fb_info *fb_info)
>   	if (spi)
>   		sprintf(text2, ", spi%d.%d at %d MHz", spi->controller->bus_num,
>   			spi_get_chipselect(spi, 0), spi->max_speed_hz / 1000000);
> +
> +#ifdef CONFIG_FB_DEVICE
>   	dev_info(fb_info->dev,

Same here with fb_info().

Best regards
Thomas

>   		 "%s frame buffer, %dx%d, %d KiB video memory%s, fps=%lu%s\n",
>   		 fb_info->fix.id, fb_info->var.xres, fb_info->var.yres,
> @@ -804,6 +814,12 @@ int fbtft_register_framebuffer(struct fb_info *fb_info)
>   		fb_info->bl_dev->props.power = BACKLIGHT_POWER_ON;
>   		fb_info->bl_dev->ops->update_status(fb_info->bl_dev);
>   	}
> +#else
> +	pr_info("%s frame buffer, %dx%d, %d KiB video memory%s, fps=%lu%s\n",
> +		fb_info->fix.id, fb_info->var.xres, fb_info->var.yres,
> +		fb_info->fix.smem_len >> 10, text1,
> +		HZ / fb_info->fbdefio->delay, text2);
> +#endif
>   
>   	return 0;
>   
> diff --git a/drivers/staging/fbtft/fbtft-sysfs.c b/drivers/staging/fbtft/fbtft-sysfs.c
> index e45c90a03a90..944f74f592d0 100644
> --- a/drivers/staging/fbtft/fbtft-sysfs.c
> +++ b/drivers/staging/fbtft/fbtft-sysfs.c
> @@ -89,6 +89,7 @@ int fbtft_gamma_parse_str(struct fbtft_par *par, u32 *curves,
>   	return ret;
>   }
>   
> +#ifdef CONFIG_FB_DEVICE
>   static ssize_t
>   sprintf_gamma(struct fbtft_par *par, u32 *curves, char *buf)
>   {
> @@ -145,6 +146,7 @@ static ssize_t show_gamma_curve(struct device *device,
>   static struct device_attribute gamma_device_attrs[] = {
>   	__ATTR(gamma, 0660, show_gamma_curve, store_gamma_curve),
>   };
> +#endif
>   
>   void fbtft_expand_debug_value(unsigned long *debug)
>   {
> @@ -173,6 +175,7 @@ void fbtft_expand_debug_value(unsigned long *debug)
>   	}
>   }
>   
> +#ifdef CONFIG_FB_DEVICE
>   static ssize_t store_debug(struct device *device,
>   			   struct device_attribute *attr,
>   			   const char *buf, size_t count)
> @@ -200,17 +203,22 @@ static ssize_t show_debug(struct device *device,
>   
>   static struct device_attribute debug_device_attr =
>   	__ATTR(debug, 0660, show_debug, store_debug);
> +#endif
>   
>   void fbtft_sysfs_init(struct fbtft_par *par)
>   {
> +#ifdef CONFIG_FB_DEVICE
>   	device_create_file(par->info->dev, &debug_device_attr);
>   	if (par->gamma.curves && par->fbtftops.set_gamma)
>   		device_create_file(par->info->dev, &gamma_device_attrs[0]);
> +#endif
>   }
>   
>   void fbtft_sysfs_exit(struct fbtft_par *par)
>   {
> +#ifdef CONFIG_FB_DEVICE
>   	device_remove_file(par->info->dev, &debug_device_attr);
>   	if (par->gamma.curves && par->fbtftops.set_gamma)
>   		device_remove_file(par->info->dev, &gamma_device_attrs[0]);
> +#endif
>   }

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)