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

["René Rebe" <rene@exactco.de>]

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?

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);
>>  }
>>  
> 

-- 
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