Re: [PATCH] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()

Seung-Woo Kim
2016-06-17T04:07:25Z

Hello Jaehoon,

On 2016년 06월 17일 10:30, Jaehoon Chung wrote:
> Hi Seung-Woo,
>
> On 06/10/2016 10:29 AM, Seung-Woo Kim wrote:
>> Hi Jaehoon,
>>
>> On 2016년 06월 09일 21:38, Jaehoon Chung wrote:
>>> Hi Seung-Woo,
>>>
>>> On 06/08/2016 01:07 PM, Seung-Woo Kim wrote:
>>>> This patch removes following UBSAN warnings in dw_mci_setup_bus().
>>>> The warnings are caused because of shift with more than 31 on 32
>>>> bit variable, so this patch fixes to shift only for less than 32.
>>>>

<snip.>

>>>>
>>>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>>>> index 2cc6123..dff045e 100644
>>>> --- a/drivers/mmc/host/dw_mmc.c
>>>> +++ b/drivers/mmc/host/dw_mmc.c
>>>> @@ -1099,7 +1099,8 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
>>>>
>>>> div = (host->bus_hz != clock) ? DIV_ROUND_UP(div, 2) : 0;
>>>>
>>>> - if ((clock << div) != slot->__clk_old || force_clkinit)
>>>> + if (((div < 32) ? (clock << div) : 0) != slot->__clk_old ||
>>>
>>> Well, we don't expect that clock is 0.
>>> if clock is 0, it should be passed to " if (!clock)"..
>>>
>>> During initializing card, clock is 400KHz or less..I understood what you want to fix.
>>> But I taught this is not correct.
>>
>> It seems slot->__clk_old is not really clock but a kind of value to
>> store both clock and div in one variable. And at least, my compiler
>> calculates right shift with more than 32 as 0. I am not sure there is
>> other proper value for the case.
>>
>> By the way, in my test environment, clock is calculated as like
>> following steps:
>> mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 400000Hz,
>> actual 400000HZ div = 250)
>> mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 200000000Hz,
>> actual 200000000HZ div = 0)
>> mmc_host mmc0: Bus speed (slot 0) = 200000000Hz (slot req 52000000Hz,
>> actual 50000000HZ div = 2)
>> mmc_host mmc0: Bus speed (slot 0) = 400000000Hz (slot req 52000000Hz,
>> actual 50000000HZ div = 4)
>> mmc_host mmc0: Bus speed (slot 0) = 400000000Hz (slot req 200000000Hz,
>> actual 200000000HZ div = 1)
>>
>> and only the first case is reported as the warning. If you let me know
>> any proper value, then I will fix with the value.
>
> I think that "clock << div" and__old_clock are used for checking whether clock is changed.
> So it doesn't need to rotate with div.
>
> Could you check the below codes?
>
> if ((clock != slot->clk_old) || force_clkinit)
> ...
>
> slot->__clk_old = clock;

From the comment about alignment of slot->__clk_old, it says that "keep
the clock with reflecting clock dividor". So to me, it is better also
adding slot->__dlv with your suggestion. I will send patch like it, soon.

Regards,
- Seung-Woo Kim

>
> Best Regards,
> Jaehoon Chung
>
>>
>> Thanks,
>> - Seung-Woo Kim
>>
>>
>>>
>>>
>>>> + force_clkinit)
>>>> dev_info(&slot->mmc->class_dev,
>>>> "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ div = %d)\n",
>>>> slot->id, host->bus_hz, clock,
>>>> @@ -1129,7 +1130,7 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
>>>> mci_send_cmd(slot, sdmmc_cmd_bits, 0);
>>>>
>>>> /* keep the clock with reflecting clock dividor */
>>>> - slot->__clk_old = clock << div;
>>>> + slot->__clk_old = (div < 32) ? (clock << div) : 0;

<snip.>

--
Seung-Woo Kim
Samsung Software R&D Center
--