linux-kernel - Re: [PATCH v2 2/3] spi: Add HiSilicon v3xx SPI NOR flash controller driver

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Date:   Fri, 31 Jan 2020 12:03:19 +0000
From:   John Garry <john.garry@...wei.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Mark Brown <broonie@...nel.org>, <chenxiang66@...ilicon.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        <liusimin4@...wei.com>, Linuxarm <linuxarm@...wei.com>,
        linux-spi <linux-spi@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        "open list:MEMORY TECHNOLOGY..." <linux-mtd@...ts.infradead.org>,
        <tudor.ambarus@...rochip.com>,
        Jiancheng Xue <xuejiancheng@...ilicon.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        wanghuiqiang <wanghuiqiang@...wei.com>, <fengsheng5@...wei.com>
Subject: Re: [PATCH v2 2/3] spi: Add HiSilicon v3xx SPI NOR flash controller
 driver

On 31/01/2020 11:39, Andy Shevchenko wrote:
> On Fri, Jan 31, 2020 at 12:08 PM John Garry <john.garry@...wei.com> wrote:
>>
>> On 13/01/2020 14:34, Andy Shevchenko wrote:
>>> On Mon, Jan 13, 2020 at 02:27:54PM +0000, Mark Brown wrote:
>>>> On Mon, Jan 13, 2020 at 04:17:32PM +0200, Andy Shevchenko wrote:
>>>>> On Mon, Jan 13, 2020 at 4:07 PM Mark Brown <broonie@...nel.org> wrote:
>>>>>> On Mon, Jan 13, 2020 at 01:01:06PM +0000, John Garry wrote:
>>>>>>> On 13/01/2020 11:42, Mark Brown wrote:
>>>>
>>>>>>>> The idiomatic approach appears to be for individual board vendors
>>>>>>>> to allocate IDs, you do end up with multiple IDs from multiple
>>>>>>>> vendors for the same thing.
>>>>
>>>>>>> But I am not sure how appropriate that same approach would be for some 3rd
>>>>>>> party memory part which we're simply wiring up on our board. Maybe it is.
>>>>
>>>>>> It seems to be quite common for Intel reference designs to assign
>>>>>> Intel IDs to non-Intel parts on the board (which is where I
>>>>>> became aware of this practice).
>>>>
>>>>> Basically vendor of component in question is responsible for ID, but
>>>>> it seems they simple don't care.
>>>>
>>>> AFAICT a lot of the time it seems to be that whoever is writing
>>>> the software ends up assigning an ID, that may not be the silicon
>>>> vendor.
>>>
>>> ...which is effectively abusing the ACPI ID allocation procedure.
>>>
>>> (And yes, Intel itself did it in the past — see badly created ACPI IDs
>>>    in the drivers)
>>>
>>
>> Hi Mark,
>>

Hi Andy,

>> About this topic of ACPI having no method to describe device buswidth in
>> the resource descriptor, it may be an idea for me to raise a Tianocore
>> feature request @ https://bugzilla.tianocore.org/
>>
> 
> The 19.6.126 describes the SPI resource, in particular:
> 
> ---8<---8<---
> DataBitLength is the size, in bits, of the smallest transfer unit for
> this connection. _LEN is automatically
> created to refer to this portion of the resource descriptor.
> ---8<---8<---
> 
> Is it what you are looking for? (As far as I know most of the
> firmwares simple abuse this field among others)

I didn't think so - I thought that there was a distinction between width 
and length in SPI terms.

So how do you find that most firmwares abuse this field? AFAICS, linux 
kernel doesn't interpret this field at all.

> 
>> There seems to be an avenue there for raising new features for the spec.
>> I (or my org) can't participate in AWSG.
> 
> But have you read 19.6.126?
> 

Maybe some clarification at least could be achieved :)

Cheers,
John