Commit 5143c953

 ("mmc: sdhci-esdhc-imx: Allow all supported
prescaler values") made it possible to set SYSCTL.SDCLKFS to 0 in SDR
mode, thus bypassing the SD clock frequency prescaler, in order to be
able to get higher SD clock frequencies in some contexts. However, that
commit missed the fact that this value is illegal on the eSDHCv3
instance of the i.MX53. This seems to be the only exception on i.MX,
this value being legal even for the eSDHCv2 instances of the i.MX53.

Fix this issue by changing the minimum prescaler value if the i.MX53
eSDHCv3 is detected. According to the i.MX53 reference manual, if
DLLCTRL[10] can be set, then the controller is eSDHCv3, else it is
eSDHCv2.

This commit fixes the following issue, which was preventing the i.MX53
Loco (IMX53QSB) board from booting Linux 4.15.0-rc5:
[    1.882668] mmcblk1: error -84 transferring data, sector 2048, nr 8, cmd response 0x900, card status 0xc00
[    2.002255] mmcblk1: error -84 transferring data, sector 2050, nr 6, cmd response 0x900, card status 0xc00
[   12.645056] mmc1: Timeout waiting for hardware interrupt.
[   12.650473] mmc1: sdhci: ============ SDHCI REGISTER DUMP ===========
[   12.656921] mmc1: sdhci: Sys addr:  0x00000000 | Version:  0x00001201
[   12.663366] mmc1: sdhci: Blk size:  0x00000004 | Blk cnt:  0x00000000
[   12.669813] mmc1: sdhci: Argument:  0x00000000 | Trn mode: 0x00000013
[   12.676258] mmc1: sdhci: Present:   0x01f8028f | Host ctl: 0x00000013
[   12.682703] mmc1: sdhci: Power:     0x00000002 | Blk gap:  0x00000000
[   12.689148] mmc1: sdhci: Wake-up:   0x00000000 | Clock:    0x0000003f
[   12.695594] mmc1: sdhci: Timeout:   0x0000008e | Int stat: 0x00000000
[   12.702039] mmc1: sdhci: Int enab:  0x107f004b | Sig enab: 0x107f004b
[   12.708485] mmc1: sdhci: AC12 err:  0x00000000 | Slot int: 0x00001201
[   12.714930] mmc1: sdhci: Caps:      0x07eb0000 | Caps_1:   0x08100810
[   12.721375] mmc1: sdhci: Cmd:       0x0000163a | Max curr: 0x00000000
[   12.727821] mmc1: sdhci: Resp[0]:   0x00000920 | Resp[1]:  0x00000000
[   12.734265] mmc1: sdhci: Resp[2]:   0x00000000 | Resp[3]:  0x00000000
[   12.740709] mmc1: sdhci: Host ctl2: 0x00000000
[   12.745157] mmc1: sdhci: ADMA Err:  0x00000001 | ADMA Ptr: 0xc8049200
[   12.751601] mmc1: sdhci: ============================================
[   12.758110] print_req_error: I/O error, dev mmcblk1, sector 2050
[   12.764135] Buffer I/O error on dev mmcblk1p1, logical block 0, lost sync page write
[   12.775163] EXT4-fs (mmcblk1p1): mounted filesystem without journal. Opts: (null)
[   12.782746] VFS: Mounted root (ext4 filesystem) on device 179:9.
[   12.789151] mmcblk1: response CRC error sending SET_BLOCK_COUNT command, card status 0x900

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>
Reported-by: Wladimir J. van der Laan <laanwj@gmail.com>
Tested-by: Wladimir J. van der Laan <laanwj@gmail.com>
Fixes: 5143c953

 ("mmc: sdhci-esdhc-imx: Allow all supported prescaler values")
Cc: <stable@vger.kernel.org> # v4.13+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>