Hi Piotr, 2017-03-07 20:00 GMT+09:00 Piotr Sroka <[email protected]>: > Hi Masahiro, > >> -----Original Message----- >> Sent: 07 March, 2017 9:03 AM >> To: Piotr Sroka >> Subject: Re: [v2 PATCH 3/3] mmc: sdhci-cadence: Update PHY delay >> configuration >> >> Hi Piotr, >> >> 2017-03-06 22:39 GMT+09:00 Piotr Sroka <[email protected]>: >> > PHY settings can be different for different platforms and SoCs. >> > Fixed PHY input delays was replaced with SoC specific compatible data. >> > DTS properties are used for configuration new PHY DLL delays. >> >> >> Probably you are familiar with this IP. >> >> Please teach me this. >> >> With this patch, we will have two groups for PHY parameters. >> >> (A) specified via a data array associated with a compatible string >> SDHCI_CDNS_PHY_DLY_SD_HS SDHCI_CDNS_PHY_DLY_SD_DEFAULT >> SDHCI_CDNS_PHY_DLY_UHS_SDR12 >> SDHCI_CDNS_PHY_DLY_UHS_SDR25 >> SDHCI_CDNS_PHY_DLY_UHS_SDR50 >> SDHCI_CDNS_PHY_DLY_UHS_DDR50 >> SDHCI_CDNS_PHY_DLY_EMMC_LEGACY >> SDHCI_CDNS_PHY_DLY_EMMC_SDR >> SDHCI_CDNS_PHY_DLY_EMMC_DDR >> >> (B) specified with DT property >> SDHCI_CDNS_PHY_DLY_SDCLK >> SDHCI_CDNS_PHY_DLY_HSMMC >> SDHCI_CDNS_PHY_DLY_STROBE >> >> I am confused. >> What is the difference between (A) and (B)? > > The first group of delays are input delays. These delays are set in current > version of sdhci-cadence driver in sdhci_cdns_phy_init function. > Following by spec: > They are provided to help in meeting timings relations between data window > and sampling clock. > The clock is fixed position in respect to the SDCLK. And the idea of sampling > is to delay and align the data to the data window. > If the default values of the delays are not sufficient/correct for the > chip/board implementation those can be adjusted > > The second group are DLL delays. > There are three delays > SDHCI_CDNS_PHY_DLY_SDCLK - sdclk delay line use to delay outgoing sdclk > signal > SDHCI_CDNS_PHY_DLY_HSMMC - sdclk delay line use to delay outgoing sdclk > signal for for HS200, HS400 and HS400ES > SDHCI_CDNS_PHY_DLY_STROBE - DLL strobe delay for HS400ES > Following by spec: > They allows to setup basic DLL parameters. In general the default values are > sufficient to start working in any speed mode. The default values of delays > and phase detect select can be adjusted depending on the chip/board > implementation.
It was not clear what makes one group different from the other. After all, parameters from both groups should be adjusted depending on chip/board implementation. > In general all PHY delays values either should be properly hardcoded in HW or > they should be properly set by FW depending on the chip/board. > So PHY driver should do not touch PHY delays at all or should set values > which are proper for specific chip/board. > > I am not sure where exactly they should be placed in dts file or in > compatible data. I am not quite sure, either. (comments are appreciated.) FWIW: The first group (data associated with compatible) allows per-chip adjustment, but not per-board. Pros are, we will not break DT compatibility, and we can avoid a list of properties difficult to understand. Cons are, we can not make fine-grained adjustment for each board. The second group (DT property) gives more flexibility for per-chip and per-board adjustment. A bad thing is we will end up with specifying a bunch of mysterious properties from DT. -- Best Regards Masahiro Yamada
