Messages in this thread | | | Date | Thu, 2 Mar 2017 13:30:13 +0100 | From | Boris Brezillon <> | Subject | Re: [PATCH 2/7] memory: atmel-ebi: Simplify SMC config code |
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Hi Alexander,
On Thu, 02 Mar 2017 13:02:16 +0100 Alexander Dahl <ada@thorsis.com> wrote:
> Hei hei, > > With > > #define ATMEL_SMC_MODE_TDF(x) (((x) - 1) << 16) > > from include/linux/mfd/syscon/atmel-smc.h you added this: > > > + ret = of_property_read_u32(np, "atmel,smc-tdf-ns", &val); > > + if (!ret) { > > + required = true; > > + ncycles = DIV_ROUND_UP(val, clk_period_ns); > > + if (ncycles > ATMEL_SMC_MODE_TDF_MAX) { > > + ret = -EINVAL; > > + goto out; > > + } > > […] > > > + smcconf->mode |= ATMEL_SMC_MODE_TDF(ncycles); > > + } > > This was the same algorithm at some other location in atmel-ebi.c > before: > > #define AT91_SMC_TDF_(x) ((((x) - 1) << 16) & AT91_SMC_TDF) > > val = DIV_ROUND_UP(timings->tdf_ns, clk_rate); > if (val > AT91_SMC_TDF_MAX) > val = AT91_SMC_TDF_MAX; > regmap_fields_write(fields->mode, conf->cs, > config->mode | AT91_SMC_TDF_(val)); > > The hardware manual (AT91SAM9G20) says values from 0 to 15 (4bit, 0x0 to > 0xF) are possible and I guess the goal is to set it to a value > corresponding to the value in ns from the dts or to 15 if it's greater > (or -EINVAL in the new version). > > However how can one set it to zero? Put in zero to the div you get zero > for ncycles or val and that goes as x into (((x) - 1) << 16) which > results in 0xF ending up as TDF_CYCLES in the mode register, right?
Indeed.
> > I can of course set a slightly greater value, which ends up in a > calculated register value of zero, but that seems more a hack to me and > is not obvious if I just look at the DTS.
No, we should fix the bug.
> > If I'm right this might be topic of another bugfix patch, or should it > be done right in a v2 of this one?
It should be done right in a v2. Something like:
if (ncycles < ATMEL_SMC_MODE_TDF_MIN) ncycles = ATMEL_SMC_MODE_TDF_MIN;
with
#define ATMEL_SMC_MODE_TDF_MIN 1
I don't think we need to backport the fix, since no-one uses this driver yet.
Thanks for this report.
Boris
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