lan8720_reset_hw() out of spec, doesn't pull low for >100us (IDFGH-3584)

[brianbienvenu]

lan8720_reset_hw() doesn't contain any delay when pulsing the reset pin low. In the real world, this makes a ~250ns wide negative pulse. The chip in production LAN8720A datasheet asks for t_rstia >100us:

The datasheet for the EOL SMSC LAN8720 also specified T11.1 Reset Pulse Width >100us.

I first noticed this issue in v4.0.1, it's unchanged in master today:
https://github.com/espressif/esp-idf/blob/master/components/esp_eth/src/esp_eth_phy_lan8720.c#L262

I added a busy wait ets_delay_us(100); to resolve this issue:

static esp_err_t lan8720_reset_hw(esp_eth_phy_t *phy)
{
    phy_lan8720_t *lan8720 = __containerof(phy, phy_lan8720_t, parent);
    if (lan8720->reset_gpio_num >= 0) {
        gpio_pad_select_gpio(lan8720->reset_gpio_num);
        gpio_set_direction(lan8720->reset_gpio_num, GPIO_MODE_OUTPUT);
        gpio_set_level(lan8720->reset_gpio_num, 0);
        ets_delay_us(100);
        gpio_set_level(lan8720->reset_gpio_num, 1);
    }
    return ESP_OK;
}

[suda-morris]

@brianbienvenu Well spotted! Will fix it ASAP.

[Alvin1Zhang]

Thanks for reporting and sorry for slow turnaround, the fix is available at 5a99038. Feel free to reopen if the issue still happens.