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    SubjectRe: [PATCH 1/3] Maple bus support for the Sega Dreamcast
    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....
    -
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