On Thu, 20 Apr 2017 00:15:07 +0200 Pavel Machek <[email protected]> wrote:
> Hi! > > > > We have some problems with fsl_ifc_nand ... in the old kernels, but > > > this one does not seem to be fixed in v4.11, either. > > > > > > UBIFS complains: > > > > > > UBIFS error (pid 931): ubifs_scan: corrupt empty space at LEB 282:252630 > > > UBIFS error (pid 931): ubifs_scanned_corruption: corruption at LEB > > > 282:252630 > > > UBIFS error (pid 931): ubifs_scanned_corruption: first 1322 bytes from > > > LEB 282:252630 > > > UBIFS error (pid 931): ubifs_scan: LEB 282 scanning failed > > > > > > Possible explanation is here: > > > > > > https://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/t/289605 > > > > > > # I see on the forum that this issue has been raised before - my > > > # understanding is that the omap2 nand driver does not perform ECC > > > # detection/correction on empty pages so when UBIFS checks the empty > > > # space data and doesn't read all 0xFF then it fails and mounts > > > # read-only. I didn't find any good solution - only a workaround to > > > # remove the UBIFS check.. > > > > > > So I checked fsl_ifc_nand.c in v4.11-rc, and yes, it seems to have the > > > same problem: > > > > > > if (errors == 15) { > > > /* > > > * Uncorrectable error. > > > * OK only if the whole page is blank. > > > * > > > * We disable ECCER reporting due to... > > > * erratum IFC-A002770 -- so report it > > > now if we > > > * see an uncorrectable error in ECCSTAT. > > > */ > > > if (!is_blank(mtd, bufnum)) > > > ctrl->nand_stat |= > > > IFC_NAND_EVTER_STAT_ECCER; > > > break; > > > } > > > > > > is_blank() checks for all 0xff's, so single-bit 0xfe in the data will > > > result in_blank() == 0 and uncorrectable error being signaled. > > > > > > Should the driver be modified somehow? > > > > Yep, nand_check_erased_ecc_chunk() [1] is here to help you check this > > case, unfortunately, it's not directly applicable here, because this > > function takes regular pointers and not __iomem ones. You'll either > > have to copy the data in an intermediate buffer before calling > > nand_check_erased_ecc_chunk(), or cast the SRAM region to a void > > pointer (which is usually not a good idea). The last option would be to > > open code nand_check_erased_ecc_chunk(), but I'd really like to avoid > > that (for maintainability concerns). > > Ok, thanks a lot for the pointer, that should be doable. > > Core of the code is: > > 1357 for (; len >= sizeof(long); > 1358 len -= sizeof(long), bitmap += sizeof(long)) { > 1359 weight = hweight_long(*((unsigned long > *)bitmap)); > 1360 bitflips += BITS_PER_LONG - weight; > 1361 if (unlikely(bitflips > bitflips_threshold)) > 1362 return -EBADMSG; > 1363 } > > Someone clearly optimized this code (took care to do long accesses > etc), but afaict hweight is quite a heavy operation: > > _GLOBAL(__arch_hweight32) > BEGIN_FTR_SECTION > b __sw_hweight32 > nop > nop > nop > nop > nop > nop > FTR_SECTION_ELSE > BEGIN_FTR_SECTION_NESTED(51) > PPC_POPCNTB(R3,R3) > srdi r4,r3,16 > add r3,r4,r3 > srdi r4,r3,8 > add r3,r4,r3 > clrldi r3,r3,64-8 > blr > FTR_SECTION_ELSE_NESTED(51) > PPC_POPCNTW(R3,R3) > clrldi r3,r3,64-8 > blr > ALT_FTR_SECTION_END_NESTED_IFCLR(CPU_FTR_POPCNTD, 51) > ALT_FTR_SECTION_END_IFCLR(CPU_FTR_POPCNTB) > EXPORT_SYMBOL(__arch_hweight32) > > Would it make sense to only do hweight if *bitmap != ~0ULL ? Would it > make sense to only check for bitflips > bitflips_threshold each 128 > bytes or something like that? I didn't go as far as you did and simply assumed hweight32/64() were already optimized. Feel free to propose extra improvements.
