linux-kernel - Re: [PATCH v2 7/9] dt-bindings: spi: mtk-snfi: Add read latch latency property

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b877af37-462e-c923-41c0-09c370062700@collabora.com>
Date:   Wed, 7 Dec 2022 10:48:44 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Xiangsheng Hou (侯祥胜) 
        <Xiangsheng.Hou@...iatek.com>,
        "miquel.raynal@...tlin.com" <miquel.raynal@...tlin.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "gch981213@...il.com" <gch981213@...il.com>,
        "vigneshr@...com" <vigneshr@...com>,
        "richard@....at" <richard@....at>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Benliang Zhao (赵本亮) 
        <Benliang.Zhao@...iatek.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Bin Zhang (章斌) <bin.zhang@...iatek.com>
Subject: Re: [PATCH v2 7/9] dt-bindings: spi: mtk-snfi: Add read latch latency
 property

Il 07/12/22 03:00, Xiangsheng Hou (侯祥胜) ha scritto:
> Hi Angelo,
> 
> On Tue, 2022-12-06 at 13:19 +0100, AngeloGioacchino Del Regno wrote:
>>>>> diff --git
>>>>> a/Documentation/devicetree/bindings/spi/mediatek,spi-
>>>>> mtk-snfi.yaml
>>>>> b/Documentation/devicetree/bindings/spi/mediatek,spi-
>>>>> mtk-snfi.yaml
>>>>> index bab23f1b11fd..6e6ff8d73fcd 100644
>>>>> --- a/Documentation/devicetree/bindings/spi/mediatek,spi-mtk-
>>>>> snfi.yaml
>>>>> +++ b/Documentation/devicetree/bindings/spi/mediatek,spi-mtk-
>>>>> snfi.yaml
>>>>> @@ -45,6 +45,13 @@ properties:
>>>>>         description: device-tree node of the accompanying ECC
>>>>> engine.
>>>>>         $ref: /schemas/types.yaml#/definitions/phandle
>>>>>     
>>>>> +  mediatek,rx-latch-latency:
>>>>> +    description: Rx delay to sample data with this value, the
>>>>> value
>>>>> +                 unit is clock cycle.
>>>>
>>>> Can't we use nanoseconds or microseconds as a unit here, instead
>>>> of
>>>> clock cycles?
>>>
>>> The clock cycle will be various with MediaTek SPI NAND controller
>>> which
>>> clock frequency can support 26/52/68/81/104MHz...
>>> It`s may be easy to configure and understand with clock cycle in
>>> unit.
>>>
>>
>> Yes, but whatever clock frequency we use, the target is to always
>> wait for
>> X nanoseconds, right?
>>
>> Waiting for 5 clock cycles at 104MHz is obviously not the same as
>> waiting
>> for the same 5 clock cycles at 26MHz: in that case, expressing the
>> value
>> in nanoseconds or microseconds would make that independent from the
>> controller's clock frequency as the calculation from `time` to
>> `cycles`
>> would be performed inside of the driver.
> 
> There have two rx related timing properties in spi-peripheral-props.
> The rx-sample-delay-ns have been used in Mediatek snfi driver to adjust
> controller sample delay.
> However another spi-rx-delay-us is in microseconds. Take 52MHz for
> example, the clock cycle will be 19.23ns which lower than 1us. This may
> not easy to by one clock cycle.
> 

I agree, but nothing prevents you from adding your own property for that.

I propose "mediatek,rx-latch-latency-ns" or "mediatek,rx-latency-ns", so that
we can specify the delay in nanoseconds: in that case, when we specify 19ns,
the driver will safely round that resulting in 52MHz == 19.23ns => 19ns valid.

Regards,
Angelo