Re: [PATCH] staging: sm750fb: do not program the PLL from an uninitialized value

[Dan Carpenter]

On Mon, Aug 17, 2026 at 05:49:33AM -0500, Yuhao Jiang wrote:
> On Mon, Aug 17, 2026 at 4:59 AM Dan Carpenter <error27@xxxxxxxxx> wrote:
> >
> > On Mon, Aug 17, 2026 at 05:13:53PM +0800, Junrui Luo via B4 Relay wrote:
> > > From: Junrui Luo <moonafterrain@xxxxxxxxxxx>
> > >
> > > sm750_calc_pll_value() writes pll->M, N, OD and POD only when its search
> > > loop finds a divider combination with 0 < M < 256, and returns 0 when
> > > there is none. ddk750_set_mode_timing() discards that return value and
> > > calls program_mode_registers() regardless, so sm750_format_pll_reg()
> > > reads the four members uninitialized and pokes them into PANEL_PLL_CTRL
> > > or CRT_PLL_CTRL. Nothing bounds var->pixclock on the way in, so a mode
> > > set can ask for a clock the loop cannot represent.
> > >
> > > Consume the return value and reject the mode; hw_sm750_crtc_set_mode()
> > > already propagates a non-zero return. Initialize the structure as well:
> > > sm750_calc_pll_value() returns early for SM750LE without writing the
> > > members, and returns non-zero on that path.
> > >
> > > Fixes: 81dee67e215b ("staging: sm750fb: add sm750 to staging")
> > > Reported-by: Yuhao Jiang <danisjiang@xxxxxxxxx>
> > > Assisted-by: Claude:claude-opus-5
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Junrui Luo <moonafterrain@xxxxxxxxxxx>
> > > ---
> >
> > Greg is not taking AI patches unless they can be tested.
> > https://lore.kernel.org/all/2026080354-skater-urgent-31b2@gregkh/
> >
> > I kind of hate AI commit messages...  They are so verbose, confident
> > and reasonable sounding.  But they don't answer any of the real
> > questions I want to know.  How did Yuhao Jiang find this bug?  What
> 
> We're working on an LLM-assisted system for vulnerability discovery,
> and this bug was found by the system and checked by me.
> 

I feel like this is always part of the story and should be told.
Regardless the firm rule is that everyone agrees on if you can't test it,
then that needs to be in the notes under the --- cut off.

(I sometimes skip this, but I've been doing this for a long long time
and everyone knows who I am.  I should follow the rules too.  #shame).

regards,
dan carpenter