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Re: [PATCH][1/2] add new Cobalt LCD framebuffer driver

To: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Subject: Re: [PATCH][1/2] add new Cobalt LCD framebuffer driver
From: Andrew Morton <akpm@linux-foundation.org>
Date: Tue, 24 Jun 2008 14:15:15 -0700
Cc: linux-fbdev-devel@lists.sourceforge.net, yoichi_yuasa@tripeaks.co.jp, ralf@linux-mips.org, linux-mips@linux-mips.org
In-reply-to: <20080624224654.1ef3d665.yoichi_yuasa@tripeaks.co.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20080624224654.1ef3d665.yoichi_yuasa@tripeaks.co.jp>
Sender: linux-mips-bounce@linux-mips.org
On Tue, 24 Jun 2008 22:46:54 +0900
Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp> wrote:

> Add new Cobalt LCD framebuffer driver.
> 
> Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
> 
>
> ...
>
> +static ssize_t cobalt_lcdfb_read(struct fb_info *info, char __user *buf,
> +                              size_t count, loff_t *ppos)
> +{
> +     char src[LCD_CHARS_MAX];
> +     unsigned long pos;
> +     int len, retval;
> +
> +     pos = *ppos;
> +     if (pos >= LCD_CHARS_MAX)
> +             return 0;
> +
> +     if (pos + count >= LCD_CHARS_MAX)
> +             count = LCD_CHARS_MAX - pos;

I think if sizeof(pos) == sizeof(count), and `count' is sufficiently
large (eg: 0xffffffff) then bad things will happen in this function.

> +     for (len = 0; len < count; len++) {
> +             retval = lcd_busy_wait(info);
> +             if (retval < 0)
> +                     break;
> +
> +             lcd_write_control(info, LCD_TEXT_POS(pos));
> +
> +             retval = lcd_busy_wait(info);
> +             if (retval < 0)
> +                     break;
> +
> +             src[len] = lcd_read_data(info);
> +             if (pos == 0x0f)
> +                     pos = 0x40;
> +             else
> +                     pos++;
> +     }
> +
> +     if (copy_to_user(buf, src, len))
> +             return -EFAULT;
> +
> +     *ppos += len;
> +
> +     return len;
> +}
> +
> +static ssize_t cobalt_lcdfb_write(struct fb_info *info, const char __user 
> *buf,
> +                               size_t count, loff_t *ppos)
> +{
> +     char dst[LCD_CHARS_MAX];
> +     unsigned long pos;
> +     int len, retval;
> +
> +     pos = *ppos;
> +     if (pos >= LCD_CHARS_MAX)
> +             return 0;
> +
> +     if (pos + count >= LCD_CHARS_MAX)
> +             count = LCD_CHARS_MAX - pos;

Ditto.

> +     if (copy_from_user(dst, buf, count))
> +             return -EFAULT;
> +
> +     for (len = 0; len < count; len++) {
> +             retval = lcd_busy_wait(info);
> +             if (retval < 0)
> +                     break;
> +
> +             lcd_write_control(info, LCD_TEXT_POS(pos));
> +
> +             retval = lcd_busy_wait(info);
> +             if (retval < 0)
> +                     break;
> +
> +             lcd_write_data(info, dst[len]);
> +             if (pos == 0x0f)
> +                     pos = 0x40;
> +             else
> +                     pos++;
> +     }
> +
> +     *ppos += len;
> +
> +     return len;
> +}

Is there any real benefit in this handling of signal_pending()?  afaict
it is done correctly, but why did we bother doing it?


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