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From: Daniel Gutson <daniel@eclypsium.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Richard Hughes <hughsient@gmail.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Tudor Ambarus <tudor.ambarus@microchip.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Boris Brezillon <bbrezillon@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Richard Weinberger <richard@nod.at>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Alex Bazhaniuk <alex@eclypsium.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH] Module argument to control whether intel-spi-pci attempts to turn the SPI flash chip writeable
Date: Thu, 30 Jul 2020 11:18:20 -0300
Message-ID: <CAFmMkTFiqDtTw2v8RJktzY--WxGd7Fdz2fKA3YxXzA8ZiDS1XQ@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a2SN3pdXV8=0jXfrsz8L64yV46fEM4zrSXfA25QK0GNuA@mail.gmail.com>

On Thu, Jul 30, 2020 at 11:09 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Thu, Jul 30, 2020 at 2:21 PM Daniel Gutson <daniel@eclypsium.com> wrote:
> > El jue., 30 jul. 2020 2:31 a. m., Greg Kroah-Hartman <gregkh@linuxfoundation.org> escribió:
> >>
> >> Again, module parameters are working on a per-chunk-of-code basis, while
> >> you want to work on a per-device basis,
> >
> >
> > I think there is a misunderstanding.  What I want is to control (turn on or off) is a very specific code snippet that provides the "functionality" of trying to turn the chip writable. The rest of the device driver is fine.
> > I assume that the one that doesn't understand is me.
> >
>
> I looked at the source code again and found that the existing module
> parameter applies to both the platform and pci device front-ends, both
> of which go through
>
>         /* Prevent writes if not explicitly enabled */
>         if (!ispi->writeable || !writeable)
>                 ispi->nor.mtd.flags &= ~MTD_WRITEABLE;
>

I think you missed
https://elixir.bootlin.com/linux/latest/source/drivers/mtd/spi-nor/controllers/intel-spi-pci.c#L44

    /* Try to make the chip read/write */
    pci_read_config_dword(pdev, BCR, &bcr);
    if (!(bcr & BCR_WPD)) {
        bcr |= BCR_WPD;
        pci_write_config_dword(pdev, BCR, bcr);
        pci_read_config_dword(pdev, BCR, &bcr);
    }

in the probe function, and is executed always and unconditionally.

/* Try to make the chip read/write */
pci_read_config_dword(pdev, BCR, &bcr);
if (!(bcr & BCR_WPD)) {
bcr |= BCR_WPD;
pci_write_config_dword(pdev, BCR, bcr);
pci_read_config_dword(pdev, BCR, &bcr);
}

> Setting the PCI device writable in hardware makes it possible to
> actually write to it *only* if the module parameter is also set to '1'.
> One might disagree with that design, but I don't think your patch
> would make it any better, it just means one would have to set
> two module parameters instead of one.
>
>      Arnd



-- 
Daniel Gutson
Argentina Site Director
Enginieering Director
Eclypsium

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Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 21:28 Daniel Gutson
2020-07-25  5:56 ` Greg Kroah-Hartman
     [not found]   ` <CAFmMkTE_dT9+WJYyb19uQ_HmgJWZSARBy6PveheQJk++NuGbkQ@mail.gmail.com>
2020-07-26  7:17     ` Greg Kroah-Hartman
     [not found]       ` <CAFmMkTFzGfFDrJrdgHztzLK2K-zBWy6T2Tv+G4-rrbVpbahkgg@mail.gmail.com>
2020-07-27 15:15         ` Arnd Bergmann
2020-07-27 15:31           ` Daniel Gutson
2020-07-29 20:54             ` Daniel Gutson
2020-07-30  5:31               ` Greg Kroah-Hartman
     [not found]                 ` <CAFmMkTHXjfG7zMr0i_h65PvjAe4opPgvzdABH8W1EUGOmcA4Zg@mail.gmail.com>
2020-07-30 14:09                   ` Arnd Bergmann
2020-07-30 14:18                     ` Daniel Gutson [this message]
2020-07-30 14:20                       ` Daniel Gutson
2020-08-03  9:57 ` Mika Westerberg
2020-08-03 10:18   ` Richard Hughes
2020-08-03 10:27     ` Mika Westerberg
2020-08-03 12:58       ` Daniel Gutson
2020-08-03 13:05         ` Mika Westerberg
2020-08-03 13:17           ` Daniel Gutson

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