linux-kernel - Re: [PATCH] staging: fbtft: core: set smem_len before fb_deferred_io

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Date:   Tue, 26 Jul 2022 19:13:48 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Peter Suti <peter.suti@...eamunlimited.com>,
        Chuansheng Liu <chuansheng.liu@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: fbtft: core: set smem_len before
 fb_deferred_io_init call

Thanks for the patch.

On Tue, Jul 26, 2022 at 10:21:13AM +0200, Peter Suti wrote:
> fb_deferred_io_init depends on smem_len being filled
> to be able to initialize the virtual page lists since
> commit 856082f021a2 ("fbdev: defio: fix the pagelist corruption")
> 

This code has changed since then so the patch needs to be updated.
The patch is still necessary but the bug will look different now
because there was a WARN_ON() added.

Currently the commit message does not say how this bug looks like to the
user.  Also the use a Fixes tag.  Something like this:

The fbtft_framebuffer_alloc() calls fb_deferred_io_init() before
initializing info->fix.smem_len.  It is set to zero by the
framebuffer_alloc() function.  It will trigger a WARN_ON() at the
start of fb_deferred_io_init() and the function will not do anything.

Fixes: 856082f021a2 ("fbdev: defio: fix the pagelist corruption")
Signed-off-by:

Make sure you CC the original author (Chuansheng Liu) so they can review
the bug fix.

Google used to give good guides for how to send a v2 patch but now the
first page is just useless.  :/

regards,
dan carpenter

> Signed-off-by: Peter Suti <peter.suti@...eamunlimited.com>
> ---
>  drivers/staging/fbtft/fbtft-core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
> index 9c4d797e7ae4..4137c1a51e1b 100644
> --- a/drivers/staging/fbtft/fbtft-core.c
> +++ b/drivers/staging/fbtft/fbtft-core.c
> @@ -656,7 +656,6 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display,
>  	fbdefio->delay =           HZ / fps;
>  	fbdefio->sort_pagelist =   true;
>  	fbdefio->deferred_io =     fbtft_deferred_io;
> -	fb_deferred_io_init(info);
>  
>  	snprintf(info->fix.id, sizeof(info->fix.id), "%s", dev->driver->name);
>  	info->fix.type =           FB_TYPE_PACKED_PIXELS;
> @@ -667,6 +666,7 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display,
>  	info->fix.line_length =    width * bpp / 8;
>  	info->fix.accel =          FB_ACCEL_NONE;
>  	info->fix.smem_len =       vmem_size;
> +	fb_deferred_io_init(info);
>  
>  	info->var.rotate =         pdata->rotate;
>  	info->var.xres =           width;
> -- 
> 2.25.1
>