netdev - Re: [PATCH net-next] cxgb4: remove bogus CHELSIO_VPD_UNIQUE

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Message-ID: <20210119140228.1f210886@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 19 Jan 2021 14:02:28 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Raju Rangoju <rajur@...lsio.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] cxgb4: remove bogus CHELSIO_VPD_UNIQUE_ID
 constant

On Sat, 16 Jan 2021 14:45:25 +0100 Heiner Kallweit wrote:
> The comment is quite weird, there is no such thing as a vendor-specific
> VPD id. 0x82 is the value of PCI_VPD_LRDT_ID_STRING. So what we are
> doing here is simply checking whether the byte at VPD address VPD_BASE
> is a valid string LRDT, same as what is done a few lines later in
> the code.
> LRDT = Large Resource Data Tag, see PCI 2.2 spec, VPD chapter
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>

Did you find this by code inspection?

> diff --git a/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c b/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
> index 2c80371f9..48f20a6a0 100644
> --- a/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
> +++ b/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
> @@ -2689,7 +2689,6 @@ void t4_get_regs(struct adapter *adap, void *buf, size_t buf_size)
>  #define VPD_BASE           0x400
>  #define VPD_BASE_OLD       0
>  #define VPD_LEN            1024
> -#define CHELSIO_VPD_UNIQUE_ID 0x82
>  
>  /**
>   * t4_eeprom_ptov - translate a physical EEPROM address to virtual
> @@ -2743,9 +2742,9 @@ int t4_seeprom_wp(struct adapter *adapter, bool enable)
>   */
>  int t4_get_raw_vpd_params(struct adapter *adapter, struct vpd_params *p)
>  {
> -	int i, ret = 0, addr;
> +	int i, ret = 0, addr = VPD_BASE;

IMHO it's more readable if the addr is set to BASE or BASE_OLD in one
place rather than having a default value at variable init which may be
overwritten.

>  	int ec, sn, pn, na;
> -	u8 *vpd, csum;
> +	u8 *vpd, csum, base_val = 0;
>  	unsigned int vpdr_len, kw_offset, id_len;
>  
>  	vpd = vmalloc(VPD_LEN);
> @@ -2755,17 +2754,12 @@ int t4_get_raw_vpd_params(struct adapter *adapter, struct vpd_params *p)
>  	/* Card information normally starts at VPD_BASE but early cards had
>  	 * it at 0.
>  	 */
> -	ret = pci_read_vpd(adapter->pdev, VPD_BASE, sizeof(u32), vpd);
> +	ret = pci_read_vpd(adapter->pdev, VPD_BASE, 1, &base_val);

Are we sure this works? I've seen silicon out there which has problems
with small PCI accesses (granted those were not VPD accesses).

>  	if (ret < 0)
>  		goto out;
>  
> -	/* The VPD shall have a unique identifier specified by the PCI SIG.
> -	 * For chelsio adapters, the identifier is 0x82. The first byte of a VPD
> -	 * shall be CHELSIO_VPD_UNIQUE_ID (0x82). The VPD programming software
> -	 * is expected to automatically put this entry at the
> -	 * beginning of the VPD.
> -	 */
> -	addr = *vpd == CHELSIO_VPD_UNIQUE_ID ? VPD_BASE : VPD_BASE_OLD;
> +	if (base_val != PCI_VPD_LRDT_ID_STRING)
> +		addr = VPD_BASE_OLD;
>  
>  	ret = pci_read_vpd(adapter->pdev, addr, VPD_LEN, vpd);
>  	if (ret < 0)