linux-kernel - Re: [PATCH RFC 1/2] Documentation: devicetree: Add property for ignoring the dummy bits sent before read transfer

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Date:   Tue, 15 Dec 2020 21:42:01 +0530
From:   Aswath Govindraju <a-govindraju@...com>
To:     Rob Herring <robh@...nel.org>
CC:     <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vadym Kochan <vadym.kochan@...ision.eu>,
        Vignesh Raghavendra <vigneshr@...com>,
        Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH RFC 1/2] Documentation: devicetree: Add property for
 ignoring the dummy bits sent before read transfer

Hi Rob,
On 15/12/20 3:53 am, Rob Herring wrote:
> On Fri, Dec 11, 2020 at 08:34:57PM +0530, Aswath Govindraju wrote:
>> Hi,
>> On 11/12/20 9:03 am, Rob Herring wrote:
>>> On Wed, Dec 09, 2020 at 11:27:07PM +0530, Aswath Govindraju wrote:
>>>> Dummy zero bits are sent before data during a read transfer. This causes
>>>> the data read to be shifted to the right. To fix this send zero bits after
>>>> the address during a read transfer.
>>>>
>>>> Add property to send zero bits after the address during a read transfer.
>>>
>>> When is this necessary? Why can't it be implied by the compatible 
>>> string which should be specific to the chip model?
>>>
>>
>> This is necessary for 93AA46A/B/C, 93LC46A/B/C, 93C46A/B/C eeproms, as
>> it can be seen in section 2.7 of [1]. We were not sure if these were the
>> only devices supported by the driver(eeprom_93xx46.c). So, in order to
>> apply this only to the above listed devices, we thought that it would be
>> better to apply this change when required by introducing a DT property.
>>
>> May I know how has this case been handled till now ??
>>
> 
> No idea. From the at93c46d (which has a compatible string) datasheet it 
> looks like it has the same thing.
> 
>> If this is required by all the devices then we can drop the property and
>> include the zero bit by default.
> 
> Looks like you need a combination of compatible strings for the above  
> devices and a property for the ORG pin state on the C devices. I assume 
> s/w needs to know if x8 or x16?
> 
Yes, there are separate properties for indicating different types of
types of eeproms.

So, do you think that it is better to add it as a seperate property??

Thanks,
Aswath
> Rob
>