linux-kernel - Re: [RFC][Patch] IBM Real-Time "SMI Free" mode driver -v4

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Message-Id: <201009241512.39311.arnd@arndb.de>
Date:	Fri, 24 Sep 2010 15:12:39 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Vernon Mauery <vernux@...ibm.com>
Cc:	Randy Dunlap <rdunlap@...otime.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Keith Mannthey <kmannth@...ibm.com>
Subject: Re: [RFC][Patch] IBM Real-Time "SMI Free" mode driver -v4

On Friday 24 September 2010, Vernon Mauery wrote:
> +enum rtl_addr_type {
> +	RTL_ADDR_TYPE_IO = 1,
> +	RTL_ADDR_TYPE_MMIO,
> +} __attribute__((packed));
> +
> +enum rtl_cmd_type {
> +	RTL_CMD_NOP = 0,
> +	RTL_CMD_ENTER_PRTM,
> +	RTL_CMD_EXIT_PRTM,
> +} __attribute__((packed));

You didn't reply to Randy's comment about the packed attribute.
I think it's rather confusing here.

> +/* The RTL table as presented by the EBDA: */
> +struct ibm_rtl_table {
> +	char signature[5];
> +	u8 version;
> +	u8 rt_status;
> +	enum rtl_cmd_type command;
> +	u8 command_status;
> +	enum rtl_addr_type cmd_address_type;
> +	u8 cmd_granularity;
> +	u8 cmd_offset;
> +	u16 reserve1;
> +	u8 cmd_port_address[4]; /* platform dependent address */
> +	u8 cmd_port_value[4];   /* platform dependent value */
> +};

I would recommend marking the member in this structure as packed instead,
not the enum.

> +#define RTL_SIGNATURE (('L'<<24)|('T'<<16)|('R'<<8)|'_')
> +
> +#define ERROR(A, B...) printk(KERN_ERR "ibm-rtl: " A, ##B )
> +#define WARNING(A, B...) printk(KERN_WARNING "ibm-rtl: " A, ##B )
> +#define DEBUG(A, B...) do { \
> +	if (debug) \
> +		printk(KERN_INFO "ibm-rtl: " A, ##B ); \
> +} while (0)

We already have wrappers for these, no need to define your own.
Please just use dev_{err,warn,dbg} or pr_{err,warning,debug}.

> +static DEFINE_MUTEX(rtl_lock);
> +static struct ibm_rtl_table __iomem *rtl_table = NULL;
> +static void __iomem *ebda_map;
> +static void __iomem *rtl_cmd_iomem_addr = NULL;
> +static u32 rtl_cmd_port_addr;
> +static enum rtl_addr_type rtl_cmd_type;
> +static u8 rtl_cmd_width;

This is somewhat inconsistent, some of these are implicitly initialized,
others have an explicit "= NULL". I would recommend leaving out the
initialization, which is the historic way to do this in the kernel.

Some people find it cleaner to define a structure containing all the
driver specific data. Since there can be only one of these devices
in your case, it's probably not important.

> +			if (rtl_cmd_type == RTL_ADDR_TYPE_MMIO)
> +				iowrite8((u8)cmd_port_val, rtl_cmd_iomem_addr);
> +			else
> +				outb((u8)cmd_port_val, rtl_cmd_port_addr);

ioread/iowrite already has the capability to use both mmio and pio
addresses. You can use ioport_map() to create an __iomem token that
corresponds to your rtl_cmd_port_addr and get rid of the rtl_cmd_type
variable.

	Arnd
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