Re: [PATCH v2] misc: aspeed-lpc-ctrl: make parameter optional

[Andrew Jeffery <andrew@aj.id.au>]

Hi Vijay,

Thanks for doing the work to fix the driver. Some minor queries/points
below.

On Thu, 17 Jan 2019, at 08:31, Vijay Khemka wrote:
> Makiing memory-region and flash as optional parameter in device
> tree if user needs to use these parameter through ioctl then
> need to define in devicetree.
> 
> Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
> ---
>  drivers/misc/aspeed-lpc-ctrl.c | 58 +++++++++++++++++++++-------------
>  1 file changed, 36 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/misc/aspeed-lpc-ctrl.c b/drivers/misc/aspeed-lpc-
> ctrl.c
> index a024f8042259..332210e06e98 100644
> --- a/drivers/misc/aspeed-lpc-ctrl.c
> +++ b/drivers/misc/aspeed-lpc-ctrl.c
> @@ -68,6 +68,7 @@ static long aspeed_lpc_ctrl_ioctl(struct file *file, 
> unsigned int cmd,
>  		unsigned long param)
>  {
>  	struct aspeed_lpc_ctrl *lpc_ctrl = file_aspeed_lpc_ctrl(file);
> +	struct device *dev = file->private_data;
>  	void __user *p = (void __user *)param;
>  	struct aspeed_lpc_ctrl_mapping map;
>  	u32 addr;
> @@ -90,6 +91,12 @@ static long aspeed_lpc_ctrl_ioctl(struct file *file, 
> unsigned int cmd,
>  		if (map.window_id != 0)
>  			return -EINVAL;
>  
> +		/* If memory-region is not described in device tree */
> +		if (!lpc_ctrl->mem_size) {
> +			dev_err(dev, "Didn't find reserved memory\n");
> +			return -EINVAL;

I feel like EINVAL isn't quite right - it's pretty generic, and the parameter
value changes its validity with the devicetree context. My gut instinct
would be to use EINVAL for parameter values that violate assumptions
of the driver rather than violate configuration of the driver. Maybe ENXIO
("No such device or address") is an improvement: "I can't map that device
because there's no such device or address"?

> +		}
> +
>  		map.size = lpc_ctrl->mem_size;
>  
>  		return copy_to_user(p, &map, sizeof(map)) ? -EFAULT : 0;
> @@ -126,9 +133,18 @@ static long aspeed_lpc_ctrl_ioctl(struct file 
> *file, unsigned int cmd,
>  			return -EINVAL;
>  
>  		if (map.window_type == ASPEED_LPC_CTRL_WINDOW_FLASH) {
> +			if (!lpc_ctrl->pnor_size) {
> +				dev_err(dev, "Didn't find host pnor flash\n");
> +				return -EINVAL;

See the error code discussion above. Also, this is userspace's error not 
the kernel's, so I think dev_err() is a bit harsh. Probably best to just let
userspace log the error if it thinks the it is concerning.

> +			}
>  			addr = lpc_ctrl->pnor_base;
>  			size = lpc_ctrl->pnor_size;
>  		} else if (map.window_type == ASPEED_LPC_CTRL_WINDOW_MEMORY) {
> +			/* If memory-region is not described in device tree */
> +			if (!lpc_ctrl->mem_size) {
> +				dev_err(dev, "Didn't find reserved memory\n");
> +				return -EINVAL;

as above.

> +			}
>  			addr = lpc_ctrl->mem_base;
>  			size = lpc_ctrl->mem_size;
>  		} else {
> @@ -196,17 +212,17 @@ static int aspeed_lpc_ctrl_probe(struct 
> platform_device *pdev)
>  	if (!lpc_ctrl)
>  		return -ENOMEM;
>  
> +	/* If flash is described in device tree then store */
>  	node = of_parse_phandle(dev->of_node, "flash", 0);
>  	if (!node) {
> -		dev_err(dev, "Didn't find host pnor flash node\n");
> -		return -ENODEV;
> -	}
> -
> -	rc = of_address_to_resource(node, 1, &resm);
> -	of_node_put(node);
> -	if (rc) {
> -		dev_err(dev, "Couldn't address to resource for flash\n");
> -		return rc;
> +		dev_dbg(dev, "Didn't find host pnor flash node\n");
> +	} else {
> +		rc = of_address_to_resource(node, 1, &resm);
> +		of_node_put(node);
> +		if (rc) {
> +			dev_err(dev, "Couldn't address to resource for flash\n");
> +			return rc;
> +		}
>  	}
>  
>  	lpc_ctrl->pnor_size = resource_size(&resm);
> @@ -214,22 +230,22 @@ static int aspeed_lpc_ctrl_probe(struct 
> platform_device *pdev)
>  
>  	dev_set_drvdata(&pdev->dev, lpc_ctrl);
>  
> +	/* If memory-region is described in device tree then store */
>  	node = of_parse_phandle(dev->of_node, "memory-region", 0);
>  	if (!node) {
> -		dev_err(dev, "Didn't find reserved memory\n");
> -		return -EINVAL;
> -	}
> +		dev_dbg(dev, "Didn't find reserved memory\n");
> +	} else {
> +		rc = of_address_to_resource(node, 0, &resm);
> +		of_node_put(node);
> +		if (rc) {
> +			dev_err(dev, "Couldn't address to resource for reserved memory\n");
> +			return -ENOMEM;

Wow, I think this is an abuse of ENOMEM. Its description is "Out of memory"
which doesn't really reflect the problem here.

Not really your fault though, maybe we'll fix that with some follow-up patches.

Cheers,

Andrew

> +		}
>  
> -	rc = of_address_to_resource(node, 0, &resm);
> -	of_node_put(node);
> -	if (rc) {
> -		dev_err(dev, "Couldn't address to resource for reserved memory\n");
> -		return -ENOMEM;
> +		lpc_ctrl->mem_size = resource_size(&resm);
> +		lpc_ctrl->mem_base = resm.start;
>  	}
>  
> -	lpc_ctrl->mem_size = resource_size(&resm);
> -	lpc_ctrl->mem_base = resm.start;
> -
>  	lpc_ctrl->regmap = syscon_node_to_regmap(
>  			pdev->dev.parent->of_node);
>  	if (IS_ERR(lpc_ctrl->regmap)) {
> @@ -258,8 +274,6 @@ static int aspeed_lpc_ctrl_probe(struct 
> platform_device *pdev)
>  		goto err;
>  	}
>  
> -	dev_info(dev, "Loaded at %pr\n", &resm);
> -
>  	return 0;
>  
>  err:
> -- 
> 2.17.1
>