linux-kernel - Re: [PATCH v3 3/4] ARM: dts: at91: sama5d2_icp: Set sst26vf064b SPI NOR flash at its maximum frequency

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Date:   Thu, 30 Mar 2023 20:41:30 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Tudor Ambarus <tudor.ambarus@...aro.org>,
        <claudiu.beznea@...rochip.com>
CC:     <alexandre.belloni@...tlin.com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        "Tudor Ambarus" <tudor.ambarus@...rochip.com>
Subject: Re: [PATCH v3 3/4] ARM: dts: at91: sama5d2_icp: Set sst26vf064b SPI
 NOR flash at its maximum frequency

On 28/03/2023 at 12:15, Tudor Ambarus wrote:
> From: Tudor Ambarus <tudor.ambarus@...rochip.com>
> 
> sama5d2_icp populates an sst26vf064b SPI NOR flash. Its maximum operating
> frequency for 2.7-3.6V is 104 MHz. As the flash is operated at 3.3V,
> increase its maximum supported frequency to 104MHz. The increasing of the
> spi-max-frequency value requires the setting of the
> "CE# Not Active Hold Time", thus set the spi-cs-setup-ns to a value of 7.
> 
> The sst26vf064b datasheet specifies just a minimum value for the
> "CE# Not Active Hold Time" and it advertises it to 5 ns. There's no
> maximum time specified. I determined experimentally that 5 ns for the
> spi-cs-setup-ns is not enough when the flash is operated close to its
> maximum frequency and tests showed that 7 ns is just fine, so set the
> spi-cs-setup-ns dt property to 7.
> 
> With the increase of frequency the reads are now faster with ~37%.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>

Tested-by: Nicolas Ferre <nicolas.ferre@...rochip.com> # on sama5d2 ICP 
board with a linux-next kernel today.

Thanks Tudor!

Best regards,
   Nicolas

> ---
>   arch/arm/boot/dts/at91-sama5d2_icp.dts | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/boot/dts/at91-sama5d2_icp.dts b/arch/arm/boot/dts/at91-sama5d2_icp.dts
> index 1346b8f2b259..999adeca6f33 100644
> --- a/arch/arm/boot/dts/at91-sama5d2_icp.dts
> +++ b/arch/arm/boot/dts/at91-sama5d2_icp.dts
> @@ -669,7 +669,8 @@ flash@0 {
>                  #size-cells = <1>;
>                  compatible = "jedec,spi-nor";
>                  reg = <0>;
> -               spi-max-frequency = <80000000>;
> +               spi-max-frequency = <104000000>;
> +               spi-cs-setup-ns = <7>;
>                  spi-tx-bus-width = <4>;
>                  spi-rx-bus-width = <4>;
>                  m25p,fast-read;
> --
> 2.40.0.348.gf938b09366-goog
> 

-- 
Nicolas Ferre