Re: [PATCH] mmc: dw_mmc: Fix the DTO timeout overflow calculation for 32-bit systems

[Vineet Gupta <Vineet.Gupta1@synopsys.com>]

Hi Evgeniy

On 02/21/2018 09:57 AM, Evgeniy Didin wrote:
> In commit 9d9491a7da2a ("mmc: dw_mmc: Fix the DTO timeout calculation") have been made
> changes which can cause multiply overflow for 32-bit systems.

Awesome, thx for quickly narrowing it down. I tried the fix and it cures my issue.

  It was caught on arc/hsdk board
> when "drto_ms" should be 671, but it was 70 and that caused a flow of stack-traces just copying
> file from mmc.

IMHO, the fragment above could be improved.

	"The broken timeout calculations caused false interrupt latency warnings
          and stacktrace splat (such as below) when accessing the SD Card."

| Running :  4M-check-reassembly-tcp-cmykw2-rotatew2.out -v0 -w1
| -  Info: Finished target initialization.
| mmcblk0: error -110 transferring data, sector 320544, nr 2048, cmd response
|  0x900, card status 0x0
| mmc_host mmc0: Bus speed (slot 0) = 50000000Hz (slot req 400000Hz, actual
| 396825HZ div = 63)
| mmc_host mmc0: Bus speed (slot 0) = 50000000Hz (slot req 25000000Hz, actual
|  25000000HZ div = 1)
| ------------[ cut here ]------------
| softirq: huh, entered softirq 6 TASKLET 6f6a9412 with preempt_count 00000101,
| exited with 00000100?
| WARNING: CPU: 2 PID: 0 at ../lib/scatterlist.c:652 sg_miter_next+0x28/0x20c
| Modules linked in:
| CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.15.0 #57
|
| Stack Trace:
|  arc_unwind_core.constprop.1+0xd0/0xf4
|  dump_stack+0x68/0x80
|  warn_slowpath_null+0x4e/0xec
|  sg_miter_next+0x28/0x20c
|  dw_mci_read_data_pio+0x44/0x190
|  dw_mmc f000a000.mmc: Unexpected interrupt latency
|   dw_mci_interrupt+0x3ee/0x530
|  __handle_irq_event_percpu+0x56/0x150
|  handle_irq_event+0x34/0x78
|  handle_level_irq+0x8e/0x120
|  generic_handle_irq+0x1c/0x2c
|  idu_cascade_isr+0x30/0x6c
|  __handle_domain_irq+0x72/0xc8
|  ret_from_exception+0x0/0x8
|---[ end trace 2a58c9af6c25fe51 ]---


> 
> Lets cast this multiply to long long int which prevents overflow.
> 
> Signed-off-by: Evgeniy Didin <Evgeniy.Didin@synopsys.com>
> CC: Alexey Brodkin <abrodkin@synopsys.com>
> CC: Douglas Anderson <dianders@chromium.org>
> CC: Ulf Hansson <ulf.hansson@linaro.org>
> CC: linux-kernel@vger.kernel.org
> CC: linux-snps-arc@lists.infradead.org

Tested-by: Vineet Gupta <vgupta@synopsys.com>
Fixes: ARC STAR 9001306872 HSDK, sdio: board crashes when copying big files

> ---
>   drivers/mmc/host/dw_mmc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 0aa39975f33b..1a0b9751c67c 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1944,7 +1944,7 @@ static void dw_mci_set_drto(struct dw_mci *host)
>   	drto_div = (mci_readl(host, CLKDIV) & 0xff) * 2;
>   	if (drto_div == 0)
>   		drto_div = 1;
> -	drto_ms = DIV_ROUND_UP(MSEC_PER_SEC * drto_clks * drto_div,
> +	drto_ms = DIV_ROUND_UP((uint64_t)MSEC_PER_SEC * drto_clks * drto_div,
>   			       host->bus_hz);
>   
>   	/* add a bit spare time */
>