Re: [PATCH v5 16/16] net: stmmac: platform: Fix PTP clock rate reading
From: Jan Petrous <jan.petrous@oss.nxp.com>
Date: 2024-11-20 12:59:58
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imx, linux-arm-kernel, linux-arm-msm, linux-devicetree, lkml
On Tue, Nov 19, 2024 at 05:09:15PM +0000, Russell King (Oracle) wrote:
On Tue, Nov 19, 2024 at 04:00:22PM +0100, Jan Petrous via B4 Relay wrote:quoted
From: "Jan Petrous (OSS)" <jan.petrous@oss.nxp.com> The stmmac driver supports many vendors SoCs using Synopsys-licensed Ethernet controller IP. Most of these vendors reuse the stmmac_platform codebase, which has a potential PTP clock initialization issue. The PTP clock rate reading might require ungating what is not provided. Fix the PTP clock initialization by enabling it immediately. Signed-off-by: Jan Petrous (OSS) <jan.petrous@oss.nxp.com> --- drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c index b1e4df1a86a0..db3e8ef4fc3a 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c@@ -632,7 +632,7 @@ stmmac_probe_config_dt(struct platform_device *pdev, u8 *mac) clk_prepare_enable(plat->pclk); /* Fall-back to main clock in case of no PTP ref is passed */ - plat->clk_ptp_ref = devm_clk_get(&pdev->dev, "ptp_ref"); + plat->clk_ptp_ref = devm_clk_get_enabled(&pdev->dev, "ptp_ref"); if (IS_ERR(plat->clk_ptp_ref)) { plat->clk_ptp_rate = clk_get_rate(plat->stmmac_clk); plat->clk_ptp_ref = NULL;Looking at where the driver makes use of clk_ptp_ref, it currently prepares and enables this clock via stmmac_open(), disables and unprepares via stmmac_release(). There could be a platform where this is being used as a power saving measure, and replacing devm_clk_get() with devm_clk_get_enabled() will defeat that. I would suggest that if you need the clock to be enabled in order to get its rate, then the call to clk_get_rate() should have the enable/disable around it to allow these other sites to work as they have done. Alternatively, we may take the view that the power saving is not necessary, or stopping the clock is not a good idea (loss of time in the 1588 block?) so the above changed would be sensible but only if the clk_prepare_enable() and clk_disable_unprepare() calls on this particular clock are also removed. I can't say which is the correct way forward.
For me it looks more conservative way to use first option = enclose the clk_get_rate() with clk_prepare_enable() and clk_disable_unprepare() as this don't change the PTP clock status for other glue drivers. BR. /Jan