Hi Masahiro, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote on Sat, 8 Sep 2018 01:10:25 +0900: > Hi Boris, > > 2018-09-07 23:53 GMT+09:00 Boris Brezillon <boris.brezillon@xxxxxxxxxxx>: > > On Fri, 7 Sep 2018 23:42:53 +0900 > > Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > > >> Hi Boris, > >> > >> 2018-09-07 23:08 GMT+09:00 Boris Brezillon <boris.brezillon@xxxxxxxxxxx>: > >> > Hi Masahiro, > >> > > >> > On Fri, 7 Sep 2018 19:56:23 +0900 > >> > Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote: > >> > > >> >> NAND devices need additional data area (OOB) for error correction, > >> >> but it is also used for Bad Block Marker (BBM). In many cases, the > >> >> first byte in OOB is used for BBM, but the location actually depends > >> >> on chip vendors. The NAND controller should preserve the precious > >> >> BBM to keep track of bad blocks. > >> >> > >> >> In Denali IP, the SPARE_AREA_SKIP_BYTES register is used to specify > >> >> the number of bytes to skip from the start of OOB. The ECC engine > >> >> will automatically skip the specified number of bytes when it gets > >> >> access to OOB area. > >> >> > >> >> The same value for SPARE_AREA_SKIP_BYTES should be used between > >> >> firmware and the operating system if you intend to use the NAND > >> >> device across the control hand-off. > >> >> > >> >> In fact, the current denali.c code expects firmware to have already > >> >> set the SPARE_AREA_SKIP_BYTES register, then reads the value out. > >> >> > >> >> If no firmware (or bootloader) has initialized the controller, the > >> >> register value is zero, which is the default after power-on-reset. > >> >> > >> >> In other words, the Linux driver cannot initialize the controller > >> >> by itself. You cannot support the reset control either because > >> >> resetting the controller will get register values lost. > >> >> > >> >> This commit adds a way to specify it via DT. If the property > >> >> "denali,oob-skip-bytes" exists, the value will be set to the register. > >> > > >> > Hm, do we really need to make this config customizable? I mean, either > >> > you have a large-page NAND (page > 512 bytes) and the 2 first bytes > >> > must be reserved for the BBM or you have a small-page NAND and the BBM > >> > is at position 4 and 5. Are you sure people configure that differently? > >> > Don't you always have SPARE_AREA_SKIP_BYTES set to 6 or 2? > >> > >> > >> As I said in the patch description, > >> I need to use the same SPARE_AREA_SKIP_BYTES value > >> across firmware, boot-loader, Linux, and whatever. > >> > >> I want to set the value to 8 for my platform > >> because the on-chip boot ROM expects 8. > >> I cannot change it since the boot ROM is hard-wired. > >> > >> > >> The boot ROM skips 8 bytes in OOB > >> when it loads images from the on-board NAND device. > >> > >> So, when I update the image from U-Boot or Linux, > >> I need to make sure to set the register to 8. > >> > >> If I update the image with a different value, > >> the Boot ROM fails to boot. > >> > >> > >> > >> When the system has booted from NAND, > >> the register is already set to 8. It works. > >> > >> However, when the system has booted from eMMC, > >> the register is not initialized by anyone. > >> I am searching for a way to set the register to 8 > >> in this case. > >> > >> > >> The boot ROM in SOCFPGA might expect a different value, > >> I am not sure. > > > > Okay, then why not having a per-compatible value if it's related to the > > BootROM? Unless the BootROM is part of the FPGA and can be > > reprogrammed. > > FPGA is unrelated here. > > Neither the boot ROM nor the Denali core is re-programmable. > > > > I hesitate to associate the number of skipped bytes > with the compatible string because it is not a parameter > of the Denali IP. > > > Rather, it is the matter of "how we use the OOB", > so I want to leave room for customization like nand-ecc-strength etc. > even if the boot ROM happens to expect a particular value. > > > If you prefer a per-compatible value, I can do that, > but I believe the NAND core and the boot ROM are orthogonal. > > > > > I'd really prefer not having a generic property that > > allows you to put anything you want. > > While I agree that the number of skipped bytes is not a parameter of the Denali IP, I also fear letting the opportunity to the user to use random values in the SPARE_AREA_SKIP_BYTES registers (and have to support them). I would also prefer a per-compatible value which is not a perfect solution neither. Thanks, Miquèl
