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From: Dmitry Torokhov on 26 Feb 2010 03:20
On Thu, Feb 25, 2010 at 08:34:42AM -0700, Rick L. Vinyard, Jr. wrote:
> Jiri Kosina wrote:
> > On Wed, 24 Feb 2010, Rick L. Vinyard, Jr. wrote:
> >
> >> The key difference is the replacement of spin_lock() with spin_trylock()
> >> such that if the non-interrupt code has already obtained the lock, the
> >> interrupt will not deadlock but instead take the else path and schedule
> >> a
> >> framebuffer update at the next interval.
> >
> > Why is _irqsave() and/or deferred work not enough? The aproach with
> > _trylock() seems to be overly complicated for no good reason (I personally
> > become very suspicious every time I see code that is using _trylock()).
> >
>
> I was concerned about _irqsave() because the lock is split across two
> functions to protect the urb after it is handed off to the usb subsystem
> with usb_submit_urb(). It's locked in g13_fb_send() and unlocked in the
> urb completion callback.
>
> As for deferred work, the g13_fb_send() is the I/O portion of the deferred
> framebuffer callback. I was concerned that without a lock one deferred
> update could hand the urb off to the usb subsystem and a second could try
> to access it before it was handed back to the driver.
>
> In this case the _trylock() would fail and in the else patch we would
> defer yet again until the next update cycle.
>

What you are looking for here is called test_and_set_bit(). Do not muddy
the waters with a lock.

--
Dmitry
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From: Pavel Machek on 3 Mar 2010 01:10
Hi!

> +#ifdef CONFIG_LOGO
> +/*
> + * This is a default logo to be loaded upon driver initialization
> + * replacing the default PicoLCD image loaded on device
> + * initialization. This is to provide the user a cue that the
> + * Linux driver is loaded and ready.
> + *
> + * This logo contains the text PicoLCD in the center with one penguin
> + * on each side of the text. The penguins are a 64x64 rendition of
> + * the default framebuffer 80x80 monochrome image scaled down and
> + * cleaned up to retain something that looks a little better than
> + * a simple scaling.
> + *
> + * This logo is a simple xbm image created in GIMP and exported.
> + * To view the image copy the following two #defines plus the
> + * picolcd_bits to an ASCII text file and save with extension
> + * .xbm, then open with GIMP or any other graphical editor
> + * such as eog that recognizes the .xbm format.
> + */
> +#define picolcd_width 256
> +#define picolcd_height 64
> +static const u8 picolcd_bits[PICOLCDFB_SIZE] = {
> + 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
> + 0xff, 0xff, 0xff, 0xf8, 0x1f, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xf8, 0x1f, 0xff, 0xff, 0xff,

Please remove this. There are less ugly/shorter ways to tell the user
device is ready.
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