On Thu, Dec 17, 2020 at 7:48 AM Aswath Govindraju <a-govindraju@xxxxxx> wrote: > > Hi Rob, > > On 15/12/20 9:42 pm, Aswath Govindraju wrote: > > 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. > > > > Here I was saying about x8 or x16 using the data-size property. ORG pin > state is implied through data-size property and an additional property > is not required for ORG pin state. Ah, I missed that property. > > > So, do you think that it is better to add it as a seperate property?? > > > > > These are the available options to my knowledge, > > 1) As you mentioned earlier all the eeprom's supported by the driver > send a dummy bit before the read data. This can be thought of a bug and > add this change as a fix for it. This might a problem for users who are > already using this driver and working around it using user space tools. > > 2) Add a special compatible string "eeprom-93xx46B", to add the extra > dummy cycle and not add an additional property. No. Genericish compatible strings are what cause the problem and this whole discussion. > 3) Add an additional property as proposed in this patch and use when > required. > > Are there any other suggestions on solving this issue?? You need a compatible string for each vendor+model. Period. Rob
