RE: [PATCH] mtd: rawnand: arasan: Fix clock rate in NV-DDR

[Amit Kumar Kumar Mahapatra <akumarma@xilinx.com>]

Hello Olga,

> -----Original Message-----
> From: Michal Simek <monstr@monstr.eu>
> Sent: Wednesday, December 1, 2021 1:46 PM
> To: Miquel Raynal <miquel.raynal@bootlin.com>; Olga Kitaina
> <okitain@gmail.com>; Amit Kumar Kumar Mahapatra
> <akumarma@xilinx.com>
> Cc: linux-mtd@lists.infradead.org; Naga Sureshkumar Relli
> <nagasure@xlnx.xilinx.com>; richard@nod.at; vigneshr@ti.com; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH] mtd: rawnand: arasan: Fix clock rate in NV-DDR
> 
> Hi,
> 
> 
> On 12/1/21 09:09, Miquel Raynal wrote:
> > Hi Olga,
> >
> > + Michal (please add him in Cc of your next iteration)
> >
> > okitain@gmail.com wrote on Tue, 30 Nov 2021 23:08:20 +0300:
> >
> >> Hi Miquel,
> >>
> >> On 30.11.2021 10:20, Miquel Raynal wrote:
> >>> Hi Olga,
> >>>
> >>> okitain@gmail.com wrote on Mon, 29 Nov 2021 21:06:05 +0300:
> >>>
> >>>> Hi Miquel,
> >>>>
> >>>> On 29.11.2021 11:55, Miquel Raynal wrote:
> >>>>> Hi Olga,
> >>>>>
> >>>>> Please add all the MTD maintainers in copy, as requested by
> >>>>> get_maintainers.pl.
> >>>>>
> >>>>> okitain@gmail.com wrote on Sat, 27 Nov 2021 21:07:58
> >>>>> +0300:
> >>>>>
> >>>>>> According to the Arasan NAND controller spec, the flash clock
> >>>>>> rate for SDR must be <= 100 MHz, while for NV-DDR it must be the
> >>>>>> same as the rate of the CLK line for the mode.
> >>>>>
> >>>>> I completely missed that, where did you get the information?
> >>>>
> >>>> The "Data Interface Transitions" chapter of the spec contains
> >>>> timings for flash clock setup in NV-DDR and NV-DDR2 modes. The "time
> period" of those clocks is equal to tCK in NV-DDR and tRC in NV-DDR2.
> >>>>
> >>>> The same chapter should have information about necessary steps to
> >>>> switch from NV-DDR to SDR, which includes setting the flash clock to
> 100 MHz.
> >>>>
> >>>>
> >>>> Just to make sure i'm not shooting myself in the foot: am I changing the
> right clock?
> >>>> The documentation points out that we have to change flash_clk,
> >>>> which i thought was
> >>>> nfc->controller_clk and set up by anand->clk, but it seems like it might
> actually be nfc->bus_clk.
> >>>
> >>> I believe I made a serious mistake, re-reading the code it feels
> >>> like I'm changing the system's clock (which basically changes
> >>> nothing in our
> >>> case) instead of changing the NAND bus clock.
> >>>
> >>>> In that case, does setting nfc->controller_clk to 100 MHz by default
> make sense?
> >>>> There isn't a hard limit on what the system clock might be (beyond
> >>>> a specific SoC), but there are timing requirements for the flash
> >>>> clock, and so setting a specific system clock frequency seems
> unnecessary for most devices.
> >>>>
> >>>
> >>> Please create a two-patch series:
> >>> 1- Setting the right clock in the current code base (inverting
> >>> bus_clk and controller_clk where relevant, setting one to 100MHz and
> >>> letting the other as it is)
> >>> 2- Changing the default NV-DDR rate based on tCK (below patch).
> >>>
> >>> Do you have the necessary hardware for testing?
> >>
> >> I'm sorry to say - I do not. The SoC this problem was initially
> >> noticed on can't run latest Linux, and even if it did I have no way of
> acquiring an NV-DDR-capable flash.
> >>
> >> Since Bootlin merged in NV-DDR support into the kernel, is it
> >> possible for you to test the next iteration of this patch series on NV-DDR
> hardware as well?
> >> Say, by purposefully preventing NV-DDR mode 5 from being chosen in
> anfc_setup_interface()?
> >
> > I don't have the hardware anymore.
> >
> > Please send a v2 with the necessary changes, then we will ask Naga (or
> > somebody else from the same team) with access to the board to test it.
> 
> Keep Amit in loop. He has access to HW and able to test.

Kindly send the next version, I have the required setup I will test it and let you know.

Regards,
Amit  
> 
> Thanks,
> Michal
> 
> --
> Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
> w: www.monstr.eu p: +42-0-721842854
> Maintainer of Linux kernel - Xilinx Microblaze Maintainer of Linux kernel -
> Xilinx Zynq ARM and ZynqMP ARM64 SoCs U-Boot custodian - Xilinx
> Microblaze/Zynq/ZynqMP/Versal SoCs

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