Re: [PATCH mm] cfag12864b: fix crash when built-in and no parport present

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 10 Feb 2007 20:51:23 +0100 Miguel Ojeda <maxextreme@gmail.com> wrote:

> Andrew, Daniel who reported the crash has tested this patch and says that it works fine avoiding it, so you can merge.
> 
> drivers-add-lcd-support-fix-crash-when-built-in-and-no-parport-present.patch
> Signed-off-by: Miguel Ojeda Sandonis <maxextreme@gmail.com>
> ---
> diff --git a/drivers/auxdisplay/cfag12864b.c b/drivers/auxdisplay/cfag12864b.c
> index 889583d..cb44cb4 100644
> --- a/drivers/auxdisplay/cfag12864b.c
> +++ b/drivers/auxdisplay/cfag12864b.c
> @@ -312,6 +312,17 @@ EXPORT_SYMBOL_GPL(cfag12864b_disable);
>  EXPORT_SYMBOL_GPL(cfag12864b_isenabled);
>  
>  /*
> + * Is the module inited?
> + */
> +
> +static unsigned char cfag12864b_inited;
> +unsigned char cfag12864b_isinited(void)
> +{
> +	return cfag12864b_inited;
> +}
> +EXPORT_SYMBOL_GPL(cfag12864b_isinited);
> +
> +/*
>   * Module Init & Exit
>   */
>  
> @@ -319,6 +330,13 @@ static int __init cfag12864b_init(void)
>  {
>  	int ret = -EINVAL;
>  
> +	/* ks0108_init() must be called first */
> +	if (!ks0108_isinited()) {
> +		printk(KERN_ERR CFAG12864B_NAME ": ERROR: "
> +			"ks0108 is not initialized\n");
> +		goto none;
> +	}
> +
>  	if (PAGE_SIZE < CFAG12864B_SIZE) {
>  		printk(KERN_ERR CFAG12864B_NAME ": ERROR: "
>  			"page size (%i) < cfag12864b size (%i)\n",
> @@ -354,6 +372,7 @@ static int __init cfag12864b_init(void)
>  	cfag12864b_clear();
>  	cfag12864b_on();
>  
> +	cfag12864b_inited = 1;
>  	return 0;
>  
>  cachealloced:
> diff --git a/drivers/auxdisplay/cfag12864bfb.c b/drivers/auxdisplay/cfag12864bfb.c
> index 94765e7..66fafbb 100644
> --- a/drivers/auxdisplay/cfag12864bfb.c
> +++ b/drivers/auxdisplay/cfag12864bfb.c
> @@ -137,7 +137,14 @@ static struct platform_device *cfag12864
>  
>  static int __init cfag12864bfb_init(void)
>  {
> -	int ret;
> +	int ret = -EINVAL;
> +
> +	/* cfag12864b_init() must be called first */
> +	if (!cfag12864b_isinited()) {
> +		printk(KERN_ERR CFAG12864BFB_NAME ": ERROR: "
> +			"cfag12864b is not initialized\n");
> +		goto none;
> +	}
>  
>  	if (cfag12864b_enable()) {
>  		printk(KERN_ERR CFAG12864BFB_NAME ": ERROR: "
> @@ -162,6 +169,7 @@ static int __init cfag12864bfb_init(void
>  		}
>  	}
>  
> +none:
>  	return ret;
>  }
>  
> diff --git a/drivers/auxdisplay/ks0108.c b/drivers/auxdisplay/ks0108.c
> index a637575..e6c3646 100644
> --- a/drivers/auxdisplay/ks0108.c
> +++ b/drivers/auxdisplay/ks0108.c
> @@ -111,6 +111,17 @@ EXPORT_SYMBOL_GPL(ks0108_address);
>  EXPORT_SYMBOL_GPL(ks0108_page);
>  
>  /*
> + * Is the module inited?
> + */
> +
> +static unsigned char ks0108_inited;
> +unsigned char ks0108_isinited(void)
> +{
> +	return ks0108_inited;
> +}
> +EXPORT_SYMBOL_GPL(ks0108_isinited);
> +
> +/*
>   * Module Init & Exit
>   */
>  
> @@ -142,6 +153,7 @@ static int __init ks0108_init(void)
>  		goto registered;
>  	}
>  
> +	ks0108_inited = 1;
>  	return 0;
>  
>  registered:
> diff --git a/include/linux/cfag12864b.h b/include/linux/cfag12864b.h
> index 0bc45e6..1605dd8 100644
> --- a/include/linux/cfag12864b.h
> +++ b/include/linux/cfag12864b.h
> @@ -73,5 +73,10 @@ extern void cfag12864b_disable(void);
>   */
>  extern unsigned char cfag12864b_isenabled(void);
>  
> +/*
> + * Is the module inited?
> + */
> +extern unsigned char cfag12864b_isinited(void);
> +
>  #endif /* _CFAG12864B_H_ */
>  
> diff --git a/include/linux/ks0108.h b/include/linux/ks0108.h
> index 8047d4b..a2c54ac 100644
> --- a/include/linux/ks0108.h
> +++ b/include/linux/ks0108.h
> @@ -43,4 +43,7 @@ extern void ks0108_address(unsigned char
>  /* Set the controller's current page (0..7) */
>  extern void ks0108_page(unsigned char page);
>  
> +/* Is the module inited? */
> +extern unsigned char ks0108_isinited(void);
> +
>  #endif /* _KS0108_H_ */

This looks hacky.

Your patch didn't include a description of the bug (please always include
such a description) so I'm not sure what's going on here.  But I'm
suspecting that module dependencies and appropriate choice of initcall
levels is the right way to fix whatever bug this is.