From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Date: Sat, 31 Jul 2010 21:21:33 +0000 Subject: Re: [PATCH 1/3] cyber2000fb: fix machine hang on module load Message-Id: <4C5493DD.7010402@garzik.org> List-Id: References: <201007312255.30729.linux@rainbow-software.org> In-Reply-To: <201007312255.30729.linux@rainbow-software.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Ondrej Zary Cc: Russell King - ARM Linux , linux-fbdev@vger.kernel.org, Kernel development list On 07/31/2010 04:55 PM, Ondrej Zary wrote: > I was testing two CyberPro 2000 based PCI cards on x86 and the machine always > hanged completely when the cyber2000fb module was loaded. It seems that the > card hangs when some registers are accessed too quickly after writing RAMDAC > control register. With this patch, both card work. > > Add delay after RAMDAC control register write to prevent hangs on module load. > > Signed-off-by: Ondrej Zary > > --- linux-2.6.35-rc2-orig/drivers/video/cyber2000fb.c 2010-06-06 05:43:24.000000000 +0200 > +++ linux-2.6.35-rc3/drivers/video/cyber2000fb.c 2010-07-27 23:12:37.000000000 +0200 > @@ -436,6 +436,8 @@ static void cyber2000fb_write_ramdac_ctr > cyber2000fb_writeb(i | 4, 0x3cf, cfb); > cyber2000fb_writeb(val, 0x3c6, cfb); > cyber2000fb_writeb(i, 0x3cf, cfb); > + /* prevent card lock-up observed on x86 with CyberPro 2000 */ > + cyber2000fb_readb(0x3cf, cfb); > } IIRC, cyber2000 is basically an S3 graphics chip. When working on s3fb, over a decade ago, ISTR needing a lot of MMIO register flushes -- dummy register reads -- to flush out just-written register writes.