Re: [PATCH 1/3] Maple bus support for the Sega Dreamcast

[Arjan van de Ven <arjan@infradead.org>]

On Sun, 9 Sep 2007 17:46:54 +0100
"Adrian McMenamin" <lkmladrian@gmail.com> wrote:

> This patch adds support for Sega's proprietary Maple bus - which is
> required to support the Dreamcast's peripherals.

Hi,

in general the code looks clean; great job on that.
A few suggestions and comments to hopefully help this driver to become
even better:

First of all, I'm a little concerned about the lack of locking that
this driver seems to have; what guarantees the integrity of the lists
used in the driver?

Second, you have a lot of use of likely() and unlikely(); so much that I think it's waaaay overkill. The code it's in generally isn't hotpath, and gcc also does a pretty decent job without giving these hints in general.



> +
> +void maple_add_packet(struct mapleq *mq)
> +{
> +	list_add((struct list_head *) mq, &maple_waitq);
> +}

for example this list.. what makes sure that no 2 pieces of code muck with it at the same time?




> +static struct maple_device *maple_alloc_dev(int port, int unit)
> +{
> +	struct maple_device *dev;
> +
> +	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +	if (unlikely(!dev))
> +		return NULL;
> +
> +	dev->port = port;
> +	dev->unit = unit;
> +	dev->mq = maple_allocq(dev);
> +
> +	if (unlikely(!dev->mq)) {

this unlikely isn't needed; gcc basically assumes that NULL pointer checks are unlikely anyway...



> +
> +static int setup_maple_commands(struct device *device, void *ignored)
> +{
> +	struct maple_device *maple_dev = to_maple_dev(device);
> +
> +	if (likely(maple_dev->interval > 0)) {
> +		if (likely(jiffies > maple_dev->when)) {

this is I think a small bug; it is for sure unsafe against jiffies wrapping... please consider using the time_before() and time_after() helpers which will make this comparison safe wrt jiffies wrapping. The same is true for all other jiffies use in the driver...


> +static irqreturn_t maplebus_dma_interrupt(int irq, void *dev_id)
> +{
> +	/* Load everything into the bottom half */
> +	schedule_work(&maple_dma_process);
> +	return IRQ_HANDLED;
> +}

I wonder if you want to at least check if the work was really for you before returning IRQ_HANDLED....