From: Boris Brezillon <boris.brezillon@free-electrons.com> To: Alexander Dahl <ada@thorsis.com> Cc: linux-arm-kernel@lists.infradead.org, Nicolas Ferre <nicolas.ferre@atmel.com>, Alexandre Belloni <alexandre.belloni@free-electrons.com>, Lee Jones <lee.jones@linaro.org>, Samuel Ortiz <sameo@linux.intel.com>, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/7] memory: atmel-ebi: Simplify SMC config code Date: Thu, 2 Mar 2017 13:30:13 +0100 [thread overview] Message-ID: <20170302133013.4dee0b4a@bbrezillon> (raw) In-Reply-To: <16727676.CMj9rWYKWZ@ada> 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
WARNING: multiple messages have this Message-ID (diff)
From: boris.brezillon@free-electrons.com (Boris Brezillon) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 2/7] memory: atmel-ebi: Simplify SMC config code Date: Thu, 2 Mar 2017 13:30:13 +0100 [thread overview] Message-ID: <20170302133013.4dee0b4a@bbrezillon> (raw) In-Reply-To: <16727676.CMj9rWYKWZ@ada> 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
next prev parent reply other threads:[~2017-03-02 12:31 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-02-20 16:54 [PATCH 0/7] memory: atmel-ebi: Add PM ops Boris Brezillon 2017-02-20 16:54 ` Boris Brezillon 2017-02-20 16:54 ` [PATCH 1/7] mfd: syscon: atmel-smc: Add new helpers to ease SMC regs manipulation Boris Brezillon 2017-02-20 16:54 ` Boris Brezillon 2017-03-14 17:00 ` Lee Jones 2017-03-14 17:00 ` Lee Jones 2017-03-14 17:21 ` Boris Brezillon 2017-03-14 17:21 ` Boris Brezillon 2017-03-15 12:19 ` Lee Jones 2017-03-15 12:19 ` Lee Jones 2017-03-15 13:21 ` Boris Brezillon 2017-03-15 13:21 ` Boris Brezillon 2017-02-20 16:54 ` [PATCH 2/7] memory: atmel-ebi: Simplify SMC config code Boris Brezillon 2017-02-20 16:54 ` Boris Brezillon 2017-03-02 12:02 ` Alexander Dahl 2017-03-02 12:02 ` Alexander Dahl 2017-03-02 12:30 ` Boris Brezillon [this message] 2017-03-02 12:30 ` Boris Brezillon 2017-07-24 9:12 ` Alexander Dahl 2017-07-24 9:12 ` Alexander Dahl 2017-07-24 19:21 ` Boris Brezillon 2017-07-24 19:21 ` Boris Brezillon 2017-07-25 11:43 ` Alexander Dahl 2017-07-25 11:43 ` Alexander Dahl 2017-02-20 16:54 ` [PATCH 3/7] memory: atmel-ebi: Stop using reg_field objects for simple things Boris Brezillon 2017-02-20 16:54 ` Boris Brezillon 2017-02-20 16:54 ` [PATCH 4/7] mfd: syscon: atmel-smc: Remove unused helpers/macros Boris Brezillon 2017-02-20 16:54 ` Boris Brezillon 2017-02-20 16:54 ` [PATCH 5/7] memory: atmel-ebi: Change naming scheme Boris Brezillon 2017-02-20 16:54 ` Boris Brezillon 2017-02-20 16:55 ` [PATCH 6/7] memory: atmel-ebi: Add missing ->numcs assignment Boris Brezillon 2017-02-20 16:55 ` Boris Brezillon 2017-02-20 16:55 ` [PATCH 7/7] memory: atmel-ebi: Add PM ops Boris Brezillon 2017-02-20 16:55 ` Boris Brezillon
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