[PATCH] clk: k210: Fix error calculation on 32bit

[Heinrich Schuchardt]

On 10/16/22 16:48, Sean Anderson wrote:
> On 10/16/22 10:40, Heinrich Schuchardt wrote:
>>
>>
>> On 10/16/22 16:19, Sean Anderson wrote:
>>> On 10/16/22 07:46, Heinrich Schuchardt wrote:
>>>>
>>>>
>>>> On 10/16/22 09:51, Michal Suchánek wrote:
>>>>> On Thu, Oct 13, 2022 at 10:34:29PM +0200, Michal Suchanek wrote:
>>>>>> k210 is 64bit but the driver and tests are also built in sandbox, and
>>>>>> that can be built 32bit.
>>>>>>
>>>>>> BIT(32) does not work on 32bit, shift before subtraction to fit into
>>>>>> 32bit integer with BIT values.
>>>>>
>>>>>
>>>>> Also see
>>>>> https://patchwork.ozlabs.org/project/uboot/patch/20221016071035.461454-1-heinrich.schuchardt@canonical.com/
>>>>>>
>>>>>> Signed-off-by: Michal Suchanek <msuchanek at suse.de>
>>>>>> ---
>>>>>>
>>>>>>   drivers/clk/clk_k210.c | 2 +-
>>>>>>   test/dm/k210_pll.c     | 2 +-
>>>>>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/clk/clk_k210.c b/drivers/clk/clk_k210.c
>>>>>> index 1961efaa5e..e85f8ae14a 100644
>>>>>> --- a/drivers/clk/clk_k210.c
>>>>>> +++ b/drivers/clk/clk_k210.c
>>>>>> @@ -846,7 +846,7 @@ again:
>>>>>>           error = DIV_ROUND_CLOSEST_ULL(f * inv_ratio, r * od);
>>>>>>           /* The lower 16 bits are spurious */
>>>>>> -        error = abs((error - BIT(32))) >> 16;
>>>>>> +        error = abs((error >> 16) - BIT(32 - 16));
>>>>
>>>>
>>>> Your patch changes the results. Replacing BIT() by BIT_ULL() does 
>>>> not change the result:
>>>>
>>>> error = -1 = 0xffffffffffffffff
>>>> before
>>>> error - BIT(32) = -4294967297 = 0xfffffffeffffffff
>>>> abs(error - BIT(32)) = 4294967297 = 0x100000001
>>>> abs(error - BIT(32)) >> 16 = 65536 = 0x10000
>>>> after
>>>> error >> 16 = -1 = 0xffffffffffffffff
>>>> (error >> 16) - BIT(32 - 16) = -65537 = 0xfffffffffffeffff
>>>> abs((error >> 16) - BIT(32 - 16)) = 65537 = 0x10001
>>>> using BIT_ULL
>>>> abs(error - BIT_ULL(32)) >> 16 = 65536 = 0x10000
>>>>
>>>> error = 70000 = 0x11170
>>>> before
>>>> error - BIT(32) = -4294897296 = 0xffffffff00011170
>>>> abs(error - BIT(32)) = 4294897296 = 0xfffeee90
>>>> abs(error - BIT(32)) >> 16 = 65534 = 0xfffe
>>>> after
>>>> error >> 16 = 1 = 0x1
>>>> (error >> 16) - BIT(32 - 16) = -65535 = 0xffffffffffff0001
>>>> abs((error >> 16) - BIT(32 - 16)) = 65535 = 0xffff
>>>> using BIT_ULL
>>>> abs(error - BIT_ULL(32)) >> 16 = 65534 = 0xfffe
>>>>
>>>> I assume this change of results is unintended.
>>>>
>>>> We also replace abs() by abs64() to get correct results on a 32bit 
>>>> system:
>>>>
>>>> error = -1 = 0xffffffffffffffff
>>>> abs(error - BIT_ULL(32)) >> 16 = 0 = 0x0
>>>> abs64(error - BIT_ULL(32)) >> 16 = 65536 = 0x10000
>>>> error = 70000 = 0x11170
>>>> abs(error - BIT_ULL(32)) >> 16 = 1 = 0x1
>>>> abs64(error - BIT_ULL(32)) >> 16 = 65534 = 0xfffe
>>>>
>>>> Best regards
>>>>
>>>> Heinrich
>>>>
>>>>>>           if (error < best_error) {
>>>>>>               best->r = r;
>>>>>> diff --git a/test/dm/k210_pll.c b/test/dm/k210_pll.c
>>>>>> index a0cc84c396..622b1c9bef 100644
>>>>>> --- a/test/dm/k210_pll.c
>>>>>> +++ b/test/dm/k210_pll.c
>>>>>> @@ -33,7 +33,7 @@ static int dm_test_k210_pll_calc_config(u32 
>>>>>> rate, u32 rate_in,
>>>>>>                   error = DIV_ROUND_CLOSEST_ULL(f * inv_ratio,
>>>>>>                                     r * od);
>>>>>>                   /* The lower 16 bits are spurious */
>>>>>> -                error = abs((error - BIT(32))) >> 16;
>>>>>> +                error = abs((error >> 16) - BIT(32 - 16));
>>>>>>                   if (error < best_error) {
>>>>>>                       best->r = r;
>>>>>>                       best->f = f;
>>>>>> -- 
>>>>>> 2.37.3
>>>>>>
>>>
>>> IMO the driver should just be changed to depend on 64-bit. The k210 
>>> is 64-bit,
>>> and I didn't write anything with 32-bit in mind.
>>
>> Michal, Simon, and I are striving to get the sandbox working on ilp32 
>> systems.
>>
>> Do you suggest to remove  the driver from sandbox_defconfig?
>>
>> This would imply that the unit test is not executed on Gitlab CI. You 
>> will still be able to execute it on the actual hardware.
> 
> It's still enabled for sandbox64, so it should still be executed there.

No, the sandbox64 is also to be compiled on ilp32. It models physical 
address extension (PAE).

Best regards

Heinrich