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Date: Mon, 28 Feb 2011 09:46:52 -0800
From: J Freyensee <james_p_freyensee@...ux.intel.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: gregkh@...e.de, linux-kernel@...r.kernel.org,
suhail.ahmed@...el.com, christophe.guerard@...el.com
Subject: Re: [PATCH 03/10] Intel PTI implementaiton of MIPI 1149.7.
On Mon, 2011-02-28 at 10:28 +0100, Arnd Bergmann wrote:
> Hi James,
>
> On Thursday 24 February 2011, james_p_freyensee@...ux.intel.com wrote:
> > From: J Freyensee <james_p_freyensee@...ux.intel.com>
> >
> > This driver is the Intel Atom implementation of MIPI P1149.7,
> > compact JTAG standard for mobile devices.
> >
> > Signed-off-by: J Freyensee <james_p_freyensee@...ux.intel.com>
> > ---
> > drivers/misc/pti.c | 890 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > 1 files changed, 890 insertions(+), 0 deletions(-)
> > create mode 100644 drivers/misc/pti.c
>
> I have no idea what a "misc" driver really is, but this one clearly isn't
> one. When you register a tty here, drivers/tty would be the right place.
It went in misc because this driver has a tty interface, char interface,
and uses other things like console. It is not just a tty-only device.
> > +
> > +struct pti_tty {
> > + struct pti_masterchannel *mc;
> > +};
> > +
> > +struct pti_dev {
> > + struct tty_port port;
> > + unsigned long pti_addr;
> > + unsigned long aperture_base;
> > + void __iomem *pti_ioaddr;
> > + unsigned long pti_iolen;
>
> pti_adr, aperture_base and pti_iolen seem to be unused in the driver, you
> only use them to get pti_ioaddr, so no need to store them.
>
> > + u8 IA_App[MAX_APP_IDS];
> > + u8 IA_OS[MAX_OS_IDS];
> > + u8 IA_Modem[MAX_MODEM_IDS];
>
> Please use lowercase identifiers.
>
> > +static DEFINE_MUTEX(alloclock);
>
> It's not really clear what this protects. Please add some comment here.
>
> > +static struct tty_driver *pti_tty_driver;
> > +
> > +static struct pti_dev *drv_data;
>
> You use drv_data both for the global structure and for local variables,
> which is rather confusing to the reader.
>
> > +static unsigned int pti_console_channel;
> > +static unsigned int pti_control_channel;
>
> These don't need to be global, because they are only used in one function
> each (besides a pointless initialization).
>
> Are you sure that you need no locking for them?
>
>
> > +static ssize_t pti_char_write(struct file *filp, const char __user *data,
> > + size_t len, loff_t *ppose)
> > +{
> > + struct pti_masterchannel *mc;
> > + void *kbuf;
> > + const char __user *tmp;
> > + size_t size = USER_COPY_SIZE, n = 0;
> > +
> > + tmp = data;
> > + mc = filp->private_data;
> > +
> > + kbuf = kmalloc(size, GFP_KERNEL);
> > + if (kbuf == NULL) {
> > + pr_err("%s(%d): buf allocation failed\n",
> > + __func__, __LINE__);
> > + return 0;
> > + }
> > +
> > + do {
> > + if (len - n > USER_COPY_SIZE)
> > + size = USER_COPY_SIZE;
> > + else
> > + size = len - n;
> > +
> > + if (copy_from_user(kbuf, tmp, size)) {
> > + kfree(kbuf);
> > + return n ? n : -EFAULT;
> > + }
> > +
> > + pti_write_to_aperture(mc, kbuf, size);
> > + n += size;
> > + tmp += size;
> > +
> > + } while (len > n);
> > +
> > + kfree(kbuf);
> > + kbuf = NULL;
> > +
> > + return len;
> > +}
>
> You write chunks of 8KB here, which sounds rather large for a serial port.
> Is that intentional? What is the typical line rate? If you need more than
> a milisecond for a single write, you should probably return a short write
> to user space or at least call cond_resched() to be more friendly to
> other tasks.
Yes, 8KB of chunks is intentional. In a side review with Alan cox, we
concluded 8KB was an appropriate size for this driver.
>
> > +static const struct tty_operations pti_tty_driver_ops = {
> > + .open = pti_tty_driver_open,
> > + .close = pti_tty_driver_close,
> > + .write = pti_tty_driver_write,
> > + .write_room = pti_tty_write_room,
> > + .install = pti_tty_install,
> > + .cleanup = pti_tty_cleanup
> > +};
> > +
> > +static const struct file_operations pti_char_driver_ops = {
> > + .owner = THIS_MODULE,
> > + .write = pti_char_write,
> > + .open = pti_char_open,
> > + .release = pti_char_release,
> > +};
> > +
> > +static struct miscdevice pti_char_driver = {
> > + .minor = MISC_DYNAMIC_MINOR,
> > + .name = CHARNAME,
> > + .fops = &pti_char_driver_ops
> > +};
> > +
>
> It's really strange to have both a tty and a character device that have similar
> operations. Why can't you have the pti_char_driver functionality in the tty driver?
>
Because that is not what the customer wanted and this is why the driver
is located in misc/ ;-).
> Arnd
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