Re: [PATCH 4.19 024/113] tty: serial: msm_serial: avoid system lockup condition
Hi!
> >> [ Upstream commit ba3684f99f1b25d2a30b6956d02d339d7acb9799 ]
> > 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.
Well, I'd be afraid that it would wait 5 seconds, not half a
second. udelay(1) may be very inaccurate.
> >>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.
Well, maybe it will be noticed, but user will have no idea what caused
it.
Pavel
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HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
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Re: [PATCH 4.19 024/113] tty: serial: msm_serial: avoid system lockup condition
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 50*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 = 50;
>> +
>> 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
>
Re: [PATCH 4.19 024/113] tty: serial: msm_serial: avoid system lockup condition
Hi!
> [ 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 50*udelay(1) is probably going to wait for more than
that.
Is 500msec reasonable with interrupts disabled?
Should it use something like 5000*udelay(100), instead, as that has
chance to result in closer-to-500msec wait?
> +++ 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 = 50;
> +
> 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?
Thanks,
Pavel
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