linux-kernel - Re: [PATCH] pci, pci-thunder-pem: Don't clobber read-only bits in bridge config registers.

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Message-ID: <20160502173408.GG24851@localhost>
Date:	Mon, 2 May 2016 12:34:08 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	David Daney <ddaney.cavm@...il.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] pci, pci-thunder-pem: Don't clobber read-only bits in
 bridge config registers.

On Mon, Apr 11, 2016 at 04:29:32PM -0700, David Daney wrote:
> From: David Daney <david.daney@...ium.com>
> 
> The 32-bit addressing modes in the I/O and Prefetchable Memory
> registers are required to be read-only.  Since the underlying access
> method allows them to be set, we must emulate their read-only nature
> and always set them.
> 
> Signed-off-by: David Daney <david.daney@...ium.com>

Applied to pci/host-thunder for v4.7, thanks, David!

> ---
>  drivers/pci/host/pci-thunder-pem.c | 42 ++++++++++++++++++++++++++++++--------
>  1 file changed, 34 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/pci/host/pci-thunder-pem.c b/drivers/pci/host/pci-thunder-pem.c
> index cabb92a..196adf6 100644
> --- a/drivers/pci/host/pci-thunder-pem.c
> +++ b/drivers/pci/host/pci-thunder-pem.c
> @@ -153,11 +153,11 @@ static int thunder_pem_config_read(struct pci_bus *bus, unsigned int devfn,
>   * reserved bits, this makes the code simpler and is OK as the bits
>   * are not affected by writing zeros to them.
>   */
> -static u32 thunder_pem_bridge_w1c_bits(int where)
> +static u32 thunder_pem_bridge_w1c_bits(u64 where_aligned)
>  {
>  	u32 w1c_bits = 0;
>  
> -	switch (where & ~3) {
> +	switch (where_aligned) {
>  	case 0x04: /* Command/Status */
>  	case 0x1c: /* Base and I/O Limit/Secondary Status */
>  		w1c_bits = 0xff000000;
> @@ -184,12 +184,34 @@ static u32 thunder_pem_bridge_w1c_bits(int where)
>  	return w1c_bits;
>  }
>  
> +/* Some bits must be written to one so they appear to be read-only. */
> +static u32 thunder_pem_bridge_w1_bits(u64 where_aligned)
> +{
> +	u32 w1_bits;
> +
> +	switch (where_aligned) {
> +	case 0x1c: /* I/O Base / I/O Limit, Secondary Status*/
> +		/* Force 32-bit I/O addressing. */
> +		w1_bits = 0x0101;
> +		break;
> +	case 0x24: /* Prefetchable Memory Base / Prefetchable Memory Limit */
> +		/* Force 64-bit addressing */
> +		w1_bits = 0x00010001;
> +		break;
> +	default:
> +		w1_bits = 0;
> +		break;
> +	}
> +	return w1_bits;
> +}
> +
>  static int thunder_pem_bridge_write(struct pci_bus *bus, unsigned int devfn,
>  				    int where, int size, u32 val)
>  {
>  	struct gen_pci *pci = bus->sysdata;
>  	struct thunder_pem_pci *pem_pci;
>  	u64 write_val, read_val;
> +	u64 where_aligned = where & ~3ull;
>  	u32 mask = 0;
>  
>  	pem_pci = container_of(pci, struct thunder_pem_pci, gen_pci);
> @@ -205,8 +227,7 @@ static int thunder_pem_bridge_write(struct pci_bus *bus, unsigned int devfn,
>  	 */
>  	switch (size) {
>  	case 1:
> -		read_val = where & ~3ull;
> -		writeq(read_val, pem_pci->pem_reg_base + PEM_CFG_RD);
> +		writeq(where_aligned, pem_pci->pem_reg_base + PEM_CFG_RD);
>  		read_val = readq(pem_pci->pem_reg_base + PEM_CFG_RD);
>  		read_val >>= 32;
>  		mask = ~(0xff << (8 * (where & 3)));
> @@ -215,8 +236,7 @@ static int thunder_pem_bridge_write(struct pci_bus *bus, unsigned int devfn,
>  		val |= (u32)read_val;
>  		break;
>  	case 2:
> -		read_val = where & ~3ull;
> -		writeq(read_val, pem_pci->pem_reg_base + PEM_CFG_RD);
> +		writeq(where_aligned, pem_pci->pem_reg_base + PEM_CFG_RD);
>  		read_val = readq(pem_pci->pem_reg_base + PEM_CFG_RD);
>  		read_val >>= 32;
>  		mask = ~(0xffff << (8 * (where & 3)));
> @@ -244,11 +264,17 @@ static int thunder_pem_bridge_write(struct pci_bus *bus, unsigned int devfn,
>  	}
>  
>  	/*
> +	 * Some bits must be read-only with value of one.  Since the
> +	 * access method allows these to be cleared if a zero is
> +	 * written, force them to one before writing.
> +	 */
> +	val |= thunder_pem_bridge_w1_bits(where_aligned);
> +
> +	/*
>  	 * Low order bits are the config address, the high order 32
>  	 * bits are the data to be written.
>  	 */
> -	write_val = where & ~3ull;
> -	write_val |= (((u64)val) << 32);
> +	write_val = (((u64)val) << 32) | where_aligned;
>  	writeq(write_val, pem_pci->pem_reg_base + PEM_CFG_WR);
>  	return PCIBIOS_SUCCESSFUL;
>  }
> -- 
> 1.8.3.1
> 
> --
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