From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marek Vasut Date: Tue, 4 Jun 2019 15:26:06 +0200 Subject: [U-Boot] [PATCH] mmc: Avoid HS400 mode when accessing boot partitions In-Reply-To: <43c3efe1-55cf-91e3-34c3-c509d0a7207d@ti.com> References: <20190531132244.29719-1-marek.vasut+renesas@gmail.com> <43c3efe1-55cf-91e3-34c3-c509d0a7207d@ti.com> Message-ID: <4690f000-38f8-c69f-bc15-702e9d00b14c@gmail.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de On 6/4/19 1:22 PM, Faiz Abbas wrote: > Hi Marek, Peng, Hi, > On 03/06/19 12:04 PM, Peng Fan wrote: >> >>> Subject: [PATCH] mmc: Avoid HS400 mode when accessing boot partitions >>> >>> According to JEDEC JESD84-B51.pdf section 6.3.3 Boot operation , >>> HS200 & HS400 mode is not supported during boot operation. The U-Boot >>> code currently only applies this restriction to HS200 mode, extend this to >>> HS400 mode as well. > The spec in section 6.3.3 (according to my understanding) is talking > about "boot operation" which is a way of getting data from the the eMMC > without going through the Device identification mode (Section 6.4.4) > i.e. without sending any commands. All the host has to do is hold the > command line low in Pre-Idle mode to automatically receive data at the > preconfigured frequency and bus width. > > When U-boot is accessing the partition, it has already gone through the > Device identification mode and is in data transfer mode (i.e. it needs > to send commands for read/write to happen). In this case, we need to > switch the partition in Extended CSD to access the boot partition > (Section 6.2.5). The spec doesn't say anything about HS200 and HS400 not > being supported here. > > Also, I don't see linux kernel switching down speed when trying to > access a boot partition (unless its being very sneaky about it). So if > you are seeing issues with accessing boot partitions at HS200/HS400 then > you should probably look at how linux code is working instead. Did you practically verify this ? In my case, the boot partition access fails in HS200/HS400 mode (samsung and sandisk emmc, but I'd have to check the exact part number). commit 01298da31d92ecc46cf9130d8cff68bc51698197 mmc: Change mode when switching to a boot partition seems to confirm that too. If nothing else, this patch should go in for the sake of consistency. -- Best regards, Marek Vasut