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 ?
Guenter
