Re: [PATCH] Module argument to control whether intel-spi-pci attempts to turn the SPI flash chip writeable

From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Daniel Gutson <daniel.gutson@eclypsium.com>
Cc: Richard Hughes <hughsient@gmail.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Boris Brezillon <bbrezillon@kernel.org>,
	Richard Weinberger <richard@nod.at>,
	Tudor Ambarus <tudor.ambarus@microchip.com>,
	linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-mtd@lists.infradead.org,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Alex Bazhaniuk <alex@eclypsium.com>
Subject: Re: [PATCH] Module argument to control whether intel-spi-pci attempts to turn the SPI flash chip writeable
Date: Mon, 3 Aug 2020 12:57:20 +0300	[thread overview]
Message-ID: <20200803095720.GC1375436@lahna.fi.intel.com> (raw)
In-Reply-To: <20200724212853.11601-1-daniel.gutson@eclypsium.com>

Hi,

Sorry for the delay, I was on vacation.

On Fri, Jul 24, 2020 at 06:28:53PM -0300, Daniel Gutson wrote:
> Currently, intel-spi has a module argument that controls whether the driver
> attempts to turn the SPI flash chip writeable. The default value
> is FALSE (don't try to make it writeable).
> However, this flag applies only for a number of devices, coming from the
> platform driver, whereas the devices detected through the PCI driver
> (intel-spi-pci) are not subject to this check since the configuration
> takes place in intel-spi-pci which doesn't have an argument.
> 
> That's why I propose this patch to add such argument to intel-spi-pci,
> so the user can control whether the driver tries to make the chip
> writeable or not, being the default FALSE as is the argument of
> intel-spi.
> 
> Signed-off-by: Daniel Gutson <daniel.gutson@eclypsium.com>
> ---
>  drivers/mtd/spi-nor/controllers/intel-spi-pci.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/controllers/intel-spi-pci.c b/drivers/mtd/spi-nor/controllers/intel-spi-pci.c
> index 81329f680bec..77e57450f166 100644
> --- a/drivers/mtd/spi-nor/controllers/intel-spi-pci.c
> +++ b/drivers/mtd/spi-nor/controllers/intel-spi-pci.c
> @@ -24,6 +24,10 @@ static const struct intel_spi_boardinfo cnl_info = {
>  	.type = INTEL_SPI_CNL,
>  };
>  
> +static bool writeable;
> +module_param(writeable, bool, 0);
> +MODULE_PARM_DESC(writeable, "Enable write access to SPI flash chip (default=0)");

I think instead of this we should simply make it so that the driver
never tries to make the chip writable.

> +
>  static int intel_spi_pci_probe(struct pci_dev *pdev,
>  			       const struct pci_device_id *id)
>  {
> @@ -41,12 +45,14 @@ static int intel_spi_pci_probe(struct pci_dev *pdev,
>  	if (!info)
>  		return -ENOMEM;
>  
> -	/* 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);
> +	if (writeable) {
> +		/* 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);
> +		}
>  	}
>  	info->writeable = !!(bcr & BCR_WPD);

So here we just read the BCR register and then set info->writeable based
on its value.

Then it is up to the BIOS to enable this if it allows writing the flash
chip from the OS side.

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