Hi Guenter, On Sun, Aug 3, 2025 at 1:16 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > On 8/2/25 12:26, Lad, Prabhakar wrote: > > 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? > > > > No, during initialization, and have no set_timeout function. max_hw_heartbeat_ms > is not supposed to change during runtime. If you do change it, the results > are undefined. > Thank you for the clarification. Ive done the changes as suggested. I will send a v3 soon. Cheers, Prabhakar
