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SubjectRe: [PATCH v2] MIPS: ralink: fix booting on mt7621
From
Date
Hi Neil,


On 20/03/18 08:22, NeilBrown wrote:
>
> Further testing showed that the original version of this
> patch wasn't 100% reliable. Very occasionally the read
> of SYSC_REG_CHIP_NAME0 returns garbage. Repeating the
> read seems to be reliable, but it hasn't happened enough
> for me to be completely confident.
> So this version repeats that first read.

You almost certainly need a sync() to ensure that the write to gcr_reg0
has completed before attempting to read sysc + SYSC_REG_CHIP_NAME0.

>
> Thanks,
> NeilBrown
>
>
> ----------------8<--------------------
> Since commit 3af5a67c86a3 ("MIPS: Fix early CM probing") the MT7621
> has not been able to boot.
>
> This patched caused mips_cm_probe() to be called before
> mt7621.c::proc_soc_init().
>
> prom_soc_init() has a comment explaining that mips_cm_probe()
> "wipes out the bootloader config" and means that configuration
> registers are no longer available. It has some code to re-enable
> this config.
>
> Before this re-enable code is run, the sysc register cannot be
> read, so when SYSC_REG_CHIP_NAME0 is read, a garbage value
> is returned and panic() is called.
>
> If we move the config-repair code to the top of prom_soc_init(),
> the registers can be read and boot can proceed.
>
> Very occasionally, the first register read after the reconfiguration
> returns garbage. So repeat that read to be on the safe side.
>
> Fixes: 3af5a67c86a3 ("MIPS: Fix early CM probing")
> Signed-off-by: NeilBrown <neil@brown.name>
> ---
> arch/mips/ralink/mt7621.c | 43 +++++++++++++++++++++++--------------------
> 1 file changed, 23 insertions(+), 20 deletions(-)
>
> diff --git a/arch/mips/ralink/mt7621.c b/arch/mips/ralink/mt7621.c
> index 1b274742077d..c37716407fbe 100644
> --- a/arch/mips/ralink/mt7621.c
> +++ b/arch/mips/ralink/mt7621.c
> @@ -170,6 +170,29 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
> u32 n1;
> u32 rev;
>
> + /* Early detection of CMP support */
> + mips_cm_probe();
> + mips_cpc_probe();
> +
> + if (mips_cps_numiocu(0)) {
> + /*
> + * mips_cm_probe() wipes out bootloader
> + * config for CM regions and we have to configure them
> + * again. This SoC cannot talk to pamlbus devices
> + * witout proper iocu region set up.
> + *
> + * FIXME: it would be better to do this with values
> + * from DT, but we need this very early because
> + * without this we cannot talk to pretty much anything
> + * including serial.
> + */
> + write_gcr_reg0_base(MT7621_PALMBUS_BASE);
> + write_gcr_reg0_mask(~MT7621_PALMBUS_SIZE |
> + CM_GCR_REGn_MASK_CMTGT_IOCU0);

i.e. Try putting a sync() here.

> + }
> +
> + n0 = __raw_readl(sysc + SYSC_REG_CHIP_NAME0);
> + /* Sometimes first read returns garbage, so try again to be safe */

Rather than doing this, which is a bit of a hack and there's no
guarantee the second read won't also read garbage without the barrier.

Thanks,
Matt

> n0 = __raw_readl(sysc + SYSC_REG_CHIP_NAME0);
> n1 = __raw_readl(sysc + SYSC_REG_CHIP_NAME1);
>
> @@ -194,26 +217,6 @@ void prom_soc_init(struct ralink_soc_info *soc_info)
>
> rt2880_pinmux_data = mt7621_pinmux_data;
>
> - /* Early detection of CMP support */
> - mips_cm_probe();
> - mips_cpc_probe();
> -
> - if (mips_cps_numiocu(0)) {
> - /*
> - * mips_cm_probe() wipes out bootloader
> - * config for CM regions and we have to configure them
> - * again. This SoC cannot talk to pamlbus devices
> - * witout proper iocu region set up.
> - *
> - * FIXME: it would be better to do this with values
> - * from DT, but we need this very early because
> - * without this we cannot talk to pretty much anything
> - * including serial.
> - */
> - write_gcr_reg0_base(MT7621_PALMBUS_BASE);
> - write_gcr_reg0_mask(~MT7621_PALMBUS_SIZE |
> - CM_GCR_REGn_MASK_CMTGT_IOCU0);
> - }
>
> if (!register_cps_smp_ops())
> return;
>

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