linux-kernel - Re: [PATCH v3 7/9] i2c: piix4: Add EFCH MMIO support to SMBus base address detect

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Date:   Mon, 24 Jan 2022 15:04:26 -0600
From:   Terry Bowman <Terry.Bowman@....com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-watchdog@...r.kernel.org,
        Jean Delvare <jdelvare@...e.com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Wolfram Sang <wsa@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Robert Richter <rrichter@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        sudheesh.mavila@....com,
        "Shah, Nehal-bakulchandra" <Nehal-bakulchandra.Shah@....com>,
        Basavaraj Natikar <Basavaraj.Natikar@....com>,
        Shyam Sundar S K <Shyam-sundar.S-k@....com>,
        Mario Limonciello <Mario.Limonciello@....com>
Subject: Re: [PATCH v3 7/9] i2c: piix4: Add EFCH MMIO support to SMBus base
 address detect



On 1/20/22 5:27 AM, Andy Shevchenko wrote:
> On Thu, Jan 20, 2022 at 1:07 AM Terry Bowman <terry.bowman@....com> wrote:
>>
>> The EFCH SMBus controller's base address is determined using details in
>> FCH::PM::DECODEEN[smbusasfiobase] and FCH::PM::DECODEEN[smbusasfioen].
>> This code also writes to FCH::PM::ISACONTROL[mmioen] to enable MMIO
>> decoding. These register fields were accessed using cd6h/cd7h port I/O.
>> cd6h/cd7h port I/O is no longer available in later AMD processors.
>> Change base address detection to use MMIO instead of port I/O cd6h/cd7h.
> 
> ...
> 
>> +       if (mmio_cfg.use_mmio) {
> 
>> +               iowrite32(ioread32(mmio_cfg.addr + 4) | SB800_PIIX4_FCH_PM_DECODEEN_MMIO,
>> +                         mmio_cfg.addr + 4);
> 
> Can you split this to three lines (with the help of a temporary variable)?
> 

I made these changes for upcoming v4.

>> +               smba_en_lo = ioread8(mmio_cfg.addr);
>> +               smba_en_hi = ioread8(mmio_cfg.addr + 1);
> 
> This makes me wonder if we can replace these two by defining
> 
>   u16 smba_en;
> 

Hi Alex,

I was unable to make these changes without losing readability. By using
a u16 smba_en I found casting required between u8 and u16 to access the byte 
offsets. This increased the number of lines and complexity. I should mention 
the port I/O here is fixed at a byte and does not support 16bit port I/O. 
I'll leave as-is if Ok with you.

Regards,
Terry


> (below also may be easily adjusted for it).
> 
>> +       } else {
>> +               outb_p(smb_en, SB800_PIIX4_SMB_IDX);
>> +               smba_en_lo = inb_p(SB800_PIIX4_SMB_IDX + 1);
>> +               outb_p(smb_en + 1, SB800_PIIX4_SMB_IDX);
>> +               smba_en_hi = inb_p(SB800_PIIX4_SMB_IDX + 1);
>> +       }
>>
>>         piix4_sb800_region_release(&PIIX4_dev->dev, &mmio_cfg);
>