linux-kernel - Re: [PATCH] mtd: nand: raw: brcmnand: When oops in progress use pio and interrupt polling

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Message-ID: <CAKekbeskaF90QecqArSd8xgsU3zpBMndeo3fbevRjUZRu=ZkMA@mail.gmail.com>
Date:   Thu, 16 May 2019 10:47:07 -0400
From:   Kamal Dasu <kamal.dasu@...adcom.com>
To:     Richard Weinberger <richard.weinberger@...il.com>
Cc:     Kamal Dasu <kdasu.kdev@...il.com>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Richard Weinberger <richard@....at>,
        LKML <linux-kernel@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] mtd: nand: raw: brcmnand: When oops in progress use pio
 and interrupt polling

On Mon, May 6, 2019 at 12:01 PM Richard Weinberger
<richard.weinberger@...il.com> wrote:
>
> On Wed, May 1, 2019 at 7:52 PM Kamal Dasu <kdasu.kdev@...il.com> wrote:
> >
> > If mtd_oops is in progress switch to polling for nand command completion
> > interrupts and use PIO mode wihtout DMA so that the mtd_oops buffer can
> > be completely written in the assinged nand partition. This is needed in
> > cases where the panic does not happen on cpu0 and there is only one online
> > CPU and the panic is not on cpu0.
>
> This optimization is highly specific to your hardware and AFAIK cannot
> be applied
> in general to brcmnand.
>
> So the problem you see is that depending on the oops you can no longer use dma
> or interrupts in the driver?
>
> How about adding a new flag to panic_nand_write() which tells the nand
> driver that
> this is a panic write?
> That way you can fall back to pio and polling mode without checking cpu numbers
> and oops_in_progress.
>

Thanks for your review  Richard. Will add flag to let low level
controller drivers know that that its a panic_write and make brcmnand
code more generic and simply fallback to pio and polling in such a
case. Will send a V2 patch with these recommended changes.

Thanks
Kamal

> --
> Thanks,
> //richard