Re: [PATCH] powerpc/44x: mask and shift to zero bug

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2017-08-25 at 13:33 +0300, Dan Carpenter wrote:
> My static checker complains that 0x00001800 >> 13 is zero.  Looking at
> the context, it seems like a copy and paste bug from the line below and
> probably 0x3 << 13 or 0x00006000 was intended.
> 
> Fixes: 2af59f7d5c3e ("[POWERPC] 4xx: Add 405GPr and 405EP support in boot wrapper")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> Not tested!
> 
> diff --git a/arch/powerpc/boot/4xx.c b/arch/powerpc/boot/4xx.c
> index 9d3bd4c45a24..f7da65169124 100644
> --- a/arch/powerpc/boot/4xx.c
> +++ b/arch/powerpc/boot/4xx.c
> @@ -564,7 +564,7 @@ void ibm405gp_fixup_clocks(unsigned int sys_clk, unsigned int ser_clk)
>  		fbdv = 16;
>  	cbdv = ((pllmr & 0x00060000) >> 17) + 1; /* CPU:PLB */
>  	opdv = ((pllmr & 0x00018000) >> 15) + 1; /* PLB:OPB */
> -	ppdv = ((pllmr & 0x00001800) >> 13) + 1; /* PLB:PCI */
> +	ppdv = ((pllmr & 0x00006000) >> 13) + 1; /* PLB:PCI */
>  	epdv = ((pllmr & 0x00001800) >> 11) + 2; /* PLB:EBC */
>  	udiv = ((cpc0_cr0 & 0x3e) >> 1) + 1; 

That rings a bell... Is this something we tried to fix before and had
problems ? The thing is when I opened the 405GP and EP manual PDF,
evince had memorized that this register was the last page I looked at
:-) And I don't remember how many years ago that is.

According to the 405gp spec ppdv is IBM bits 17,18 so your patch is
correct.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>