On 3/25/19 11:24 AM, BOUGH CHEN wrote: > >> -----Original Message----- >> From: Marek Vasut [mailto:marek.va...@gmail.com] >> Sent: 2019年3月18日 19:53 >> To: BOUGH CHEN <haibo.c...@nxp.com>; jh80.ch...@samsung.com; >> tr...@konsulko.com >> Cc: marek.vasut+rene...@gmail.com; Ye Li <ye...@nxp.com>; dl-uboot-imx >> <uboot-...@nxp.com>; u-boot@lists.denx.de >> Subject: Re: [PATCH] mmc: correct the HS400 initialization process >> >> On 3/18/19 9:23 AM, BOUGH CHEN wrote: >>> After the commit b9a2a0e2e9c0 ("mmc: Add support for downgrading >>> HS200/HS400 to HS mode"), it add a parameter in mmc_set_card_speed() >>> which indicates that the HS200/HS400 to HS downgrade is happening. >>> >>> During the HS400 initialization, first select to HS200, and config the >>> related clock rate, then downgrade to HS mode. So here also need to >>> config the downgrade value to be true, make sure in the function >>> mmc_set_card_speed(), after switch to HS mode, first config the clock >>> rate, then read the EXT_CSD. Otherwise read EXT_CSD in HS mode at >>> wrong clock rate, e.g. 200MHz, may lead to uncertain result. >> >> I think the fix is right, but the reasoning for it is not. >> >> If you call mmc_set_card_speed() with hsdowngrade=true, it will result in >> calling __mmc_switch() with send_status=false , which in turn means that >> after issuing the MMC_CMD_SWITCH command, the code won't poll the card >> using MMC_CMD_SEND_STATUS, but just wait a bit and then switch the bus >> properties. This is indeed required when switching bus properties. >> And that's what I think was making your card unstable. >> >> Is that the case ? > > Sorry for the tardy reply, I miss the email last week. > No, if without this patch, even I add the dealy after the switch command, > eMMC still stuck after the CMD8. > The main issue is that, in mmc_set_card_speed, if the bus mode the HS mode, > it will send CMD8 to get the EXT_CSD, but the clock is still 200MHz at that > time. > It is wrong that EMMC output data in HS mode at 200MHz.
OK, that makes sense. -- Best regards, Marek Vasut _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
