On 7/31/19 21:05, Pavel Machek wrote:
> Hi!
hi Pavel,
>
>> [ Upstream commit ba3684f99f1b25d2a30b6956d02d339d7acb9799 ]
>>
>> The function msm_wait_for_xmitr can be taken with interrupts
>> disabled. In order to avoid a potential system lockup - demonstrated
>> under stress testing conditions on SoC QCS404/5 - make sure we wait
>> for a bounded amount of time.
>>
>> Tested on SoC QCS404.
>
> How long did it take to timeout?
>
> Because... this is supposed to loop for 0.5 second with interrupts
> disabled, but 500000*udelay(1) is probably going to wait for more than
> that.
>
> Is 500msec reasonable with interrupts disabled?
considering the original unbounded definition, it is hard to determine
what would be a good amount of time to wait (msm_serial can be used for
BT comms and I am not sure how critical that link might be for different
clients..and I didnt want to create a regression hence the half a second
delay).
yeah, I don't think disabling interrupts for half a second is a good
idea on most systems hence why I chose it that big.
>
> Should it use something like 5000*udelay(100), instead, as that has
> chance to result in closer-to-500msec wait?
the half a second timeout didnt mean to be accurate but a worst case
scenario...I am not sure accuracy matters.
>
>> +++ b/drivers/tty/serial/msm_serial.c
>> @@ -383,10 +383,14 @@ static void msm_request_rx_dma(struct msm_port *msm_port, resource_size_t base)
>>
>> static inline void msm_wait_for_xmitr(struct uart_port *port)
>> {
>> + unsigned int timeout = 500000;
>> +
>> while (!(msm_read(port, UART_SR) & UART_SR_TX_EMPTY)) {
>> if (msm_read(port, UART_ISR) & UART_ISR_TX_READY)
>> break;
>> udelay(1);
>> + if (!timeout--)
>> + break;
>> }
>> msm_write(port, UART_CR_CMD_RESET_TX_READY, UART_CR);
>> }
>
> Plus, should it do some kind of dev_err() to let users know that
> something went very wrong with their serial?
I did consider this but then I thought that 1/2 second without
interrupts on the core should not go unnoticed. But I might be wrong.
>
> Thanks,
> Pavel
>
