Re: [PATCH] fbdev/ffb: fix corrupted video output on FFB1

["René Rebe" <rene@exactco.de>]

Hello again,

> On 6. Feb 2026, at 11:30, René Rebe <rene@exactco.de> wrote:
> 
> Hi,
> 
>> On 6. Feb 2026, at 11:12, Helge Deller <deller@gmx.de> wrote:
>> 
>> Hello Rene,
>> 
>> On 2/5/26 16:49, René Rebe wrote:
>>> Fix Sun FFB1 corrupted video out [1] by disabling overlay and
>>> initializing window mode to a known state. The issue never appeared on
>>> my FFB2+/vertical nor Elite3D/M6. It could also depend on the PROM
>>> version.
>>> /SUNW,ffb@1e,0: FFB at 000001fc00000000, type 11, DAC pnum[236c] rev[10] manuf_rev[4]
>>> X (II) /dev/fb0: Detected FFB1, Z-buffer, Single-buffered.
>>> X (II) /dev/fb0: BT9068 (PAC1) ramdac detected (with normal cursor control)
>>> X (II) /dev/fb0: Detected Creator/Creator3D
>>> [1] https://www.instagram.com/p/DUTcSmSjSem/
>> 
>> The patch itself seems ok.
>> But could you please link to a freely accessible website instead of Instagram?
>> I and many others don't have (and don't want) an instagram account, so
>> the link is not very useful.
> 
> Well it is more free than accessing Linux Foundation training material ;-)
> It was only for illustration purposes if someone wanted to see or follow random
> daily  development fun and not that important. Should I resend it w/o it?

While I try to influence next gen to get into OpenSource and low level programming,
how about Mastodon links?

	https://chaos.social/@ReneRebe/116023241660154102

Do you want to edit the patch or should I send a V2?

	René

> Thanks!
> René
> 
>> Helge
>> 
>>> Signed-off-by: René Rebe <rene@exactco.de>
>>> Cc: stable@kernel.org
>>> ---
>>> Tested on Sun Ultra 2 w/ FFB1 BT9068 (PAC1) ramdac running T2/Linux.
>>> Defines re-used from xf86-video-sunffb.
>>> ---
>>> diff --git a/drivers/video/fbdev/ffb.c b/drivers/video/fbdev/ffb.c
>>> index 34b6abff9493..8d77f102dd82 100644
>>> --- a/drivers/video/fbdev/ffb.c
>>> +++ b/drivers/video/fbdev/ffb.c
>>> @@ -335,6 +335,9 @@ struct ffb_dac {
>>> };
>>>   #define FFB_DAC_UCTRL 0x1001 /* User Control */
>>> +#define FFB_DAC_UCTRL_OVENAB 0x00000008 /* Overlay Enable */
>>> +#define FFB_DAC_UCTRL_WMODE 0x00000030 /* Window Mode */
>>> +#define FFB_DAC_UCTRL_WM_COMB 0x00000000 /* Window Mode = Combined */
>>> #define FFB_DAC_UCTRL_MANREV 0x00000f00 /* 4-bit Manufacturing Revision */
>>> #define FFB_DAC_UCTRL_MANREV_SHIFT 8
>>> #define FFB_DAC_TGEN 0x6000 /* Timing Generator */
>>> @@ -425,7 +428,7 @@ static void ffb_switch_from_graph(struct ffb_par *par)
>>> {
>>>  struct ffb_fbc __iomem *fbc = par->fbc;
>>>  struct ffb_dac __iomem *dac = par->dac;
>>> - unsigned long flags;
>>> + unsigned long flags, uctrl;
>>>    spin_lock_irqsave(&par->lock, flags);
>>>  FFBWait(par);
>>> @@ -442,7 +445,7 @@ static void ffb_switch_from_graph(struct ffb_par *par)
>>>  upa_writel(par->bg_cache, &fbc->bg);
>>>  FFBWait(par);
>>> - /* Disable cursor.  */
>>> + /* Disable cursor. */
>>>  upa_writel(FFB_DAC_CUR_CTRL, &dac->type2);
>>>  if (par->flags & FFB_FLAG_INVCURSOR)
>>>  upa_writel(0, &dac->value2);
>>> @@ -450,6 +453,15 @@ static void ffb_switch_from_graph(struct ffb_par *par)
>>>  upa_writel((FFB_DAC_CUR_CTRL_P0 |
>>>     FFB_DAC_CUR_CTRL_P1), &dac->value2);
>>> + /* Disable overlay and window modes. */
>>> + upa_writel(FFB_DAC_UCTRL, &dac->type);
>>> + uctrl = upa_readl(&dac->value);
>>> + uctrl &= ~FFB_DAC_UCTRL_WMODE;
>>> + uctrl |= FFB_DAC_UCTRL_WM_COMB;
>>> + uctrl &= ~FFB_DAC_UCTRL_OVENAB;
>>> + upa_writel(FFB_DAC_UCTRL, &dac->type);
>>> + upa_writel(uctrl, &dac->value);
>>> +
>>>  spin_unlock_irqrestore(&par->lock, flags);
>>> }
>>> 
>> 
> 
> -- 
> https://exactco.de • https://t2linux.com • https://patreon.com/renerebe
> 

-- 
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