Hi Guenter, On Fri, Aug 1, 2025 at 10:04 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > On 8/1/25 13:51, Lad, Prabhakar wrote: > > Hi Guenter, > > > > On Fri, Aug 1, 2025 at 7:04 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > >> > >> On 8/1/25 08:30, Lad, Prabhakar wrote: > >>> Hi Guenter, > >>> > >>> On Fri, Aug 1, 2025 at 2:52 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > >>>> > >>>> On 8/1/25 04:05, Lad, Prabhakar wrote: > >>>>> Hi Wolfram, > >>>>> > >>>>> Thank you for the review. > >>>>> > >>>>> On Fri, Aug 1, 2025 at 5:10 AM Wolfram Sang > >>>>> <wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote: > >>>>>> > >>>>>> On Tue, Jul 29, 2025 at 04:59:13PM +0100, Prabhakar wrote: > >>>>>>> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx> > >>>>>>> > >>>>>>> Update the watchdog minimum timeout value to be derived from > >>>>>>> `max_hw_heartbeat_ms` using `DIV_ROUND_UP()` to ensure a valid and > >>>>>>> consistent minimum timeout in seconds. > >>>>>> > >>>>>> I don't understand this change. Why is the _minimum_ timeout based on > >>>>>> the _maximum_ heartbeat? > >>>>>> > >>>>> The reason for deriving min_timeout from max_hw_heartbeat_ms is to > >>>>> ensure the minimum watchdog period (in seconds) is compatible with the > >>>>> underlying hardware. > >>>>> > >>>>> max_hw_heartbeat_ms is calculated as: > >>>>> max_hw_heartbeat_ms = (1000 * 16384 * cks_div) / clk_rate; > >>>>> > >>>>> This value varies by SoC: > >>>>> RZ/T2H: cks_div = 8192, clk ≈ 62.5 MHz -> max_hw_heartbeat_ms ~ 2147ms > >>>>> RZ/V2H: cks_div = 256, clk ≈ 240 MHz -> max_hw_heartbeat_ms ~ 174ms > >>>>> > >>>>> Since min_timeout is in seconds, setting it to: > >>>>> min_timeout = DIV_ROUND_UP(max_hw_heartbeat_ms, 1000); > >>>>> > >>>>> ensures: > >>>>> The minimum timeout period is never less than what the hardware can support. > >>>>> - For T2H, this results in a min_timeout of 3s (2147ms -> 3s). > >>>>> - For V2H, it’s just 1s (174ms -> 1s). > >>>>> > >>>> > >>>> Sorry, I completely fail to understand the logic. > >>>> > >>>> If the maximum timeout is, say, 2 seconds, why would the hardware > >>>> not be able to support a timeout of 1 second ? > >>>> > >>> The watchdog timer on RZ/V2H (and RZ/T2H) is a 14 bit down counter. On > >>> initialization the down counters on the SoCs are configured to the max > >>> down counter. On RZ/V2H down counter value 4194304 (which evaluates to > >>> 174ms) is and on RZ/T2H is 134217728 (which evaluates to 2147ms). The > >>> board will be reset when we get an underflow error. > >>> > >>> So for example on T2H consider this example: > >>> - down counter is 134217728 > >>> - min_timeout is set to 1 in the driver > >>> - When set WDIOC_SETTIMEOUT to 1 > >>> In this case the board will be reset after 2147ms, i.e. incorrect > >>> behaviour as we expect the board to be reset after 1 sec. Hence the > >>> min_timeout is set to 3s (2147ms -> 3s). > >>> > >>> Please let me know if my understanding of min_timeout is incorrect here. > >>> > >> > >> The driver is missing a set_timeout function. It should set RZ/T2H > >> to 62514079 if a timeout of 1 second is configured. > >> > > Ok, you mean to handle the 1sec case, introduce the set_timeout for RZ/T2H SoC. > > > > Although we cannot achieve the exact 1sec case as we can have only 4 > > timeout period options (number of cycles): > > > > 1] For TIMEOUT_CYCLES = 1024 > > - (1000×1024×8192)/62500000 = 134.22 ms > > 2] For TIMEOUT_CYCLES = 4096 > > - (1000×4096×8192)/62500000 = 536.87 ms > > 3] For TIMEOUT_CYCLES = 8192 > > - (1000×8192×8192)/62500000 = 1,073.74 ms > > 4] For TIMEOUT_CYCLES = 16384 > > - (1000×16384×8192)/62500000 = 2,147.48 ms > > > > So to handle the 1sec case I'll set the timeout period to 8192 with > > which we get a timeout of 1,073.74 ms. > > > > Just four possible values to set the hardware timeout ? That is an odd > hardware. In that case, you could also set the period to 1024 or 4096 > and set max_hw_heartbeat_ms accordingly. That would avoid the rounding > error. > Yes sadly we have four timeout periods only. To clarify, you mean to set `max_hw_heartbeat_ms` in set_timeout? Cheers, Prabhakar
