Messages in this thread | | | Date | Wed, 13 Dec 2023 15:01:09 +0000 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH] net: mdio: mdio-bcm-unimac: Delay before first poll |
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On Wed, Dec 13, 2023 at 11:57:52AM +0100, Andrew Lunn wrote: > On Tue, Dec 12, 2023 at 04:02:49PM -0800, Justin Chen wrote: > > With a clock interval of 400 nsec and a 64 bit transactions (32 bit > > preamble & 16 bit control & 16 bit data), it is reasonable to assume > > the mdio transaction will take 25.6 usec. Add a 30 usec delay before > > the first poll to reduce the chance of a 1000-2000 usec sleep. > > #define MDIO_C45 0 > > suggests the hardware can do C45? The timing works out different then. > Maybe add a comment by the udelay() that is assumes C22, to give a > clue to somebody who is adding C45 support the delay needs to be > re-evaluated.
Note, however, that the driver only supports C22 operations (it only populates the read|write functions, not the c45 variants).
However, it doesn't explicitly set the MDIO_C22 bit in the configuration register, so what ends up being spat out on the bus would be dependent on the boot loader configuration.
However, I'm wondering why unimac_mdio_poll() isn't written as (based on current code):
return read_poll_timeout(unimac_mdio_readl(priv, MDIO_CMD), val, !(val & MDIO_START_BUSY), 2000, 2000000);
rather than open-coding the io polling.
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