linux-kernel - Re: [PATCH v1 3/6] ARM: dts: lan966x: add all flexcom usart nodes

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Message-ID: <d7d17a2156a9591ad4c19ef912189a98@walle.cc>
Date:   Tue, 22 Mar 2022 22:39:07 +0100
From:   Michael Walle <michael@...le.cc>
To:     Claudiu.Beznea@...rochip.com
Cc:     Kavyasree.Kotagiri@...rochip.com, Nicolas.Ferre@...rochip.com,
        arnd@...db.de, olof@...om.net, soc@...nel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        krzysztof.kozlowski@...onical.com, alexandre.belloni@...tlin.com
Subject: Re: [PATCH v1 3/6] ARM: dts: lan966x: add all flexcom usart nodes

Am 2022-03-18 13:17, schrieb Claudiu.Beznea@...rochip.com:
> On 07.03.2022 14:04, Michael Walle wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know 
>> the
>> content is safe
>> 
>> Am 2022-03-07 12:53, schrieb Claudiu.Beznea@...rochip.com:
>>> On 04.03.2022 13:01, Michael Walle wrote:
>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you 
>>>> know
>>>> the
>>>> content is safe
>>>> 
>>>> Hi,
>>>> 
>>>> thanks for the quick review.
>>>> 
>>>> Am 2022-03-04 09:30, schrieb Claudiu.Beznea@...rochip.com:
>>>>> On 03.03.2022 18:03, Michael Walle wrote:
>>>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you
>>>>>> know
>>>>>> the content is safe
>>>>>> 
>>>>>> Add all the usart nodes for the flexcom block. There was already
>>>>>> an usart node for the flexcom3 block. But it missed the DMA
>>>>>> channels.
>>>>> 
>>>>> And it would be good to go though a different patch.
>>>> 
>>>> sure
>>>> 
>>>>>> Although the DMA channels are specified, DMA is not
>>>>>> enabled by default because break detection doesn't work with DMA.
>>>>>> 
>>>>>> Keep the nodes disabled by default.
>>>>>> 
>>>>>> Signed-off-by: Michael Walle <michael@...le.cc>
>>>>>> ---
>>>>>>  arch/arm/boot/dts/lan966x.dtsi | 55
>>>>>> ++++++++++++++++++++++++++++++++++
>>>>>>  1 file changed, 55 insertions(+)
>>>>>> 
>>>>>> diff --git a/arch/arm/boot/dts/lan966x.dtsi
>>>>>> b/arch/arm/boot/dts/lan966x.dtsi
>>>>>> index a7d46a2ca058..bea69b6d2749 100644
>>>>>> --- a/arch/arm/boot/dts/lan966x.dtsi
>>>>>> +++ b/arch/arm/boot/dts/lan966x.dtsi
>>>>>> @@ -92,6 +92,19 @@ flx0: flexcom@...40000 {
>>>>>>                         #size-cells = <1>;
>>>>>>                         ranges = <0x0 0xe0040000 0x800>;
>>>>>>                         status = "disabled";
>>>>>> +
>>>>>> +                       usart0: serial@200 {
>>>>>> +                               compatible =
>>>>>> "atmel,at91sam9260-usart";
>>>>> 
>>>>> Are the usart blocks in lan966x 1:1 compatible with what is is
>>>>> sam9260?
>>>>> In
>>>>> case not it may worth to have a new compatible here, for lan966x,
>>>>> such
>>>>> that
>>>>> when new features will be implemented in usart driver for lan966x 
>>>>> the
>>>>> old
>>>>> DT (this one) will work with the new kernel implementation.
>>>> 
>>>> During my review of the inital dtsi patch, I've asked the same
>>>> question
>>>> [1]
>>>> and I was told they are the same.
>>>> 
>>>> At least this exact usart compatible is already in this file. I was
>>>> under
>>>> the impression, that was the least controversial compatible :)
>>> 
>>> OK.
>>> 
>>>> 
>>>> But you'll need to tell me if they are the same or not, I don't have
>>>> any clue what microchip has reused.
>>> 
>>> From software point of view comparing registers should be good, as 
>>> far
>>> as I
>>> can tell. All AT91 datasheet should be available. I though you have
>>> checked
>>> one against LAN966. At the moment I don't have a DS for LAN966. I'll
>>> find
>>> one and have a look.
>> 
>> So my train of thought was like: even if the registers are the same I
>> cannot be sure that it is the exact same IP and will behave the same.
>> Therefore, it is something only microchip can answer.
>> 
>> You can find the registers at
>> https://microchip-ung.github.io/lan9668_reginfo/reginfo_LAN9668.html
>> 
>> I'm not aware of any "classic" datasheet.
> 
> You can find all AT91 datasheet on Microchip web site [1].
> 
> Simple register comparison b/w register mapping at [2] and SAMA5D2
> datasheet [3] (which uses the same compatible),  SAM9X60 datasheet [3] 
> and
> SAMA7G5 datasheet (not public at the moment) brings up a difference at
> register FLEX_US_CR (bits 16, 17) which are not available on SAMA5D2,
> SAM9X60 or SAMA7G5. Unless this is a mistake on documentation at [2] I 
> say
> it needs a new compatible.

I can't follow you here. These bits are already used in the current UART
driver and are supported on the LAN966X. So if anything, SAMA5D2, 
SAM9X60
and SAMA7G5 need a new compatible, no?

-michael

> Kavya, could you confirm this?
> 
> Thank you,
> Claudiu Beznea
> 
> [1] https://www.microchip.com/
> [2] 
> https://microchip-ung.github.io/lan9668_reginfo/reginfo_LAN9668.html
> [3] 
> http://ww1.microchip.com/downloads/en/devicedoc/ds60001476b.pdf#G22.2193277
> [4]
> https://ww1.microchip.com/downloads/aemDocuments/documents/MPU32/ProductDocuments/DataSheets/SAM9X60-Data-Sheet-DS60001579E.pdf
> 
>> 
>> -michael