From: Conor Dooley The Candence GEM IP has a configuration parameter which determines the source of the clock used for the timestamp unit (if it is enabled), switching it between using the pclk and a dedicated input. When ptp support was added to the macb driver, a new tsu_clk was added to represent the dedicated input. While this is understanble, I think it is bug prone and that the tsu_clk should represent whatever clock is used for the timerstamper and not just that specific input. >From a devicetree point of view, it doesn't really matter if the tsu_clk represents a physical clock or a conceptual clock, because the clock configuration is determined when the IP is instantiated not at runtime. >From a driver point of view, the benefit of taking the conceptual approach is avoiding misconfiguring the driver when the hardware supports ptp (and it is set as a capability in the relevant per-device structure) but no tsu_clk is provided in devicetree. At the moment, the timestamper will be registered and programmed with an increment that reflects the pclk in these cases, but will malfunction if the pclk and tsu_clk frequencies do not match. Out of the devices that claim MACB_CAPS_GEM_HAS_PTP the fu540, mpfs, sama5d2 and sama7g5-emac (but not sama7g5-gem) are at risk of having this problem with the in-kernel devicetrees. It may be that these platforms actually do use the pclk for the timestamper (either by supplying pclk to the tsu_clk input of the IP, or by having the IP block configured to use pclk instead of the tsu_clk input), but at least mpfs is wrong though, it does not use pclk for the tsu_clk, so the driver is registering the ptp clock incorrectly. Add a warning if no tsu_clk is provided on a platform that uses the timerstamper, to encourage people to specifically provide a tsu_clk and avoid silently registering the timerstamper with the wrong clock While this changes the meaning of the devicetree property, it is backwards compatible as there's no functional change for platforms that didn't provide a tsu_clk and the changed meaning of providing a tsu_clk in the devicetree does not impact platforms that already provided one as the decision about the tsu clock source is at IP instantiation time rather than at runtime. Signed-off-by: Conor Dooley --- drivers/net/ethernet/cadence/macb_main.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c index ca141f8935d48..5c24ea146d63d 100644 --- a/drivers/net/ethernet/cadence/macb_main.c +++ b/drivers/net/ethernet/cadence/macb_main.c @@ -3534,6 +3534,7 @@ static unsigned int gem_get_tsu_rate(struct macb *bp) else if (!IS_ERR(bp->pclk)) { tsu_clk = bp->pclk; tsu_rate = clk_get_rate(tsu_clk); + dev_warn(&bp->pdev->dev, "devicetree missing tsu_clk, using pclk as fallback\n"); } else return -ENOTSUPP; return tsu_rate; -- 2.51.0