linux-kernel - Re: [PATCH v6 2/2] memory: pl353: Add driver for arm pl353 static memory controller

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Message-ID: <CAGnW=BY=vAOYMuK7My-g6+YOBEnbkRaY4mwpGUE9TexA9_GsFg@mail.gmail.com>
Date:	Tue, 28 Apr 2015 21:28:42 +0530
From:	punnaiah choudary kalluri <punnaia@...inx.com>
To:	Ben Shelton <ben.shelton@...com>
Cc:	Punnaiah Choudary Kalluri <punnaiah.choudary.kalluri@...inx.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	"michal.simek@...inx.com" <michal.simek@...inx.com>,
	Grant Likely <grant.likely@...aro.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jason@...edaemon.net" <jason@...edaemon.net>,
	"ezequiel.garcia@...e-electrons.com" 
	<ezequiel.garcia@...e-electrons.com>,
	Arnd Bergmann <arnd@...db.de>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	"artem.bityutskiy@...ux.intel.com" <artem.bityutskiy@...ux.intel.com>,
	"jussi.kivilinna@....fi" <jussi.kivilinna@....fi>,
	Alexandre Courbot <acourbot@...dia.com>,
	"Khoronzhuk, Ivan" <ivan.khoronzhuk@...com>,
	"joern@...fs.org" <joern@...fs.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Punnaiah Choudary <kpc528@...il.com>
Subject: Re: [PATCH v6 2/2] memory: pl353: Add driver for arm pl353 static
 memory controller

Hi Ben,

  I will take care of the boundary conditions for both lower and upper
limits and update the patches accordingly.

Thanks,
Punnaiah

On Tue, Apr 28, 2015 at 8:41 PM, Ben Shelton <ben.shelton@...com> wrote:
> Hi Punnaiah,
>
>> +/**
>> + * pl353_smc_set_cycles - Set memory timing parameters
>> + * @dev:     Pointer to the device struct
>> + * @t0:      t_rc            read cycle time
>> + * @t1:      t_wc            write cycle time
>> + * @t2:      t_rea/t_ceoe    output enable assertion delay
>> + * @t3:      t_wp            write enable deassertion delay
>> + * @t4:      t_clr/t_pc      page cycle time
>> + * @t5:      t_ar/t_ta       ID read time/turnaround time
>> + * @t6:      t_rr            busy to RE timing
>> + *
>> + * Sets NAND chip specific timing parameters.
>> + */
>> +void pl353_smc_set_cycles(struct device *dev, u32 t0, u32 t1, u32 t2, u32 t3,
>> +                       u32 t4, u32 t5, u32 t6)
>> +{
>> +     struct pl353_smc_data *pl353_smc = dev_get_drvdata(dev);
>> +
>> +     t0 &= PL353_SMC_SET_CYCLES_T0_MASK;
>> +     t1 = (t1 & PL353_SMC_SET_CYCLES_T1_MASK) <<
>> +                     PL353_SMC_SET_CYCLES_T1_SHIFT;
>> +     t2 = (t2 & PL353_SMC_SET_CYCLES_T2_MASK) <<
>> +                     PL353_SMC_SET_CYCLES_T2_SHIFT;
>> +     t3 = (t3 & PL353_SMC_SET_CYCLES_T3_MASK) <<
>> +                     PL353_SMC_SET_CYCLES_T3_SHIFT;
>> +     t4 = (t4 & PL353_SMC_SET_CYCLES_T4_MASK) <<
>> +                     PL353_SMC_SET_CYCLES_T4_SHIFT;
>> +     t5 = (t5 & PL353_SMC_SET_CYCLES_T5_MASK) <<
>> +                     PL353_SMC_SET_CYCLES_T5_SHIFT;
>> +     t6 = (t6 & PL353_SMC_SET_CYCLES_T6_MASK) <<
>> +                     PL353_SMC_SET_CYCLES_T6_SHIFT;
>
> Right now, if the caller (i.e. the PL353 NAND driver) passes in a value for any
> of the timing parameters that is too large, it will be truncated with the
> corresponding mask and then saved, resulting in unexpected behavior.  I saw
> this when the PL353 NAND driver tried to set t_rc and t_wc to 17 cycles, which
> does not fit in the 4-bit fields for those values -- it got clipped to 4 bits
> and stored as 1 cycle, which made communication with the NAND chip fail and
> time out.
>
> It would be good to sanity-check each timing here, and rather than returning
> void, return a return code indicating success or failure (e.g. -EINVAL for
> invalid timings).
>
> Note also that truncation isn't the only thing to check for here.  The PL350
> r2p1 datasheet lists a "Minimum permitted value" for each of these timing
> values.
>
>> +
>> +     t0 |= t1 | t2 | t3 | t4 | t5 | t6;
>> +
>> +     writel(t0, pl353_smc->base + PL353_SMC_SET_CYCLES_OFFS);
>> +     writel(PL353_SMC_DC_UPT_NAND_REGS, pl353_smc->base +
>> +            PL353_SMC_DIRECT_CMD_OFFS);
>> +}
>> +EXPORT_SYMBOL_GPL(pl353_smc_set_cycles);
>> +
>
> Thanks,
> Ben
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