linux-kernel - Re: [PATCH 07/15] PCI: brcmstb: Add control of rescal reset

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Message-ID: <c76cc2e6-fcc5-5d42-5ff1-770a99cb9b13@gmail.com>
Date:   Mon, 25 May 2020 09:58:33 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jim Quinlan <james.quinlan@...adcom.com>,
        Philipp Zabel <pza@...gutronix.de>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" 
        <linux-pci@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/15] PCI: brcmstb: Add control of rescal reset



On 5/21/2020 2:48 PM, Jim Quinlan wrote:
> On Wed, May 20, 2020 at 3:27 AM Philipp Zabel <pza@...gutronix.de> wrote:
>>
>> Hi Jim,
>>
>> On Tue, May 19, 2020 at 04:34:05PM -0400, Jim Quinlan wrote:
>>> From: Jim Quinlan <jquinlan@...adcom.com>
>>>
>>> Some STB chips have a special purpose reset controller named
>>> RESCAL (reset calibration).  This commit adds the control
>>> of RESCAL as well as the ability to start and stop its
>>> operation for PCIe HW.
>>>
>>> Signed-off-by: Jim Quinlan <jquinlan@...adcom.com>
>>> ---
>>>  drivers/pci/controller/pcie-brcmstb.c | 81 ++++++++++++++++++++++++++-
>>>  1 file changed, 80 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
>>> index 2c470104ba38..0787e8f6f7e5 100644
>>> --- a/drivers/pci/controller/pcie-brcmstb.c
>>> +++ b/drivers/pci/controller/pcie-brcmstb.c
>> [...]
>>> @@ -1100,6 +1164,21 @@ static int brcm_pcie_probe(struct platform_device *pdev)
>>>               dev_err(&pdev->dev, "could not enable clock\n");
>>>               return ret;
>>>       }
>>> +     pcie->rescal = devm_reset_control_get_shared(&pdev->dev, "rescal");
>>> +     if (IS_ERR(pcie->rescal)) {
>>> +             if (PTR_ERR(pcie->rescal) == -EPROBE_DEFER)
>>> +                     return -EPROBE_DEFER;
>>> +             pcie->rescal = NULL;
>>
>> This is effectively an optional reset control, so it is better to use:
>> ↵
>>         pcie->rescal = devm_reset_control_get_optional_shared(&pdev->dev,
>>                                                               "rescal");↵
>>         if (IS_ERR(pcie->rescal))
>>                 return PTR_ERR(pcie->rescal);
>>
>>> +     } else {
>>> +             ret = reset_control_deassert(pcie->rescal);
>>> +             if (ret)
>>> +                     dev_err(&pdev->dev, "failed to deassert 'rescal'\n");
>>> +     }
>>
>> reset_control_* can handle rstc == NULL parameters for optional reset
>> controls, so this can be done unconditionally:
>>
>>         ret = reset_control_deassert(pcie->rescal);↵
>>         if (ret)↵
>>                 dev_err(&pdev->dev, "failed to deassert 'rescal'\n");↵
>>
>> Is rescal handled by the reset-brcmstb-rescal driver? Since that only
>> implements the .reset op, I would expect reset_control_reset() here.
> Where exactly?  "reset.h" says that "Calling reset_control_rese()t is
> not allowed on a shared reset control." so I'm not sure why  you would
> want me to invoke it.

Yes this is handled by drivers/reset/reset-brcmstb-rescal.c which only
implements a .reset() callback, what would be the appropriate API usage
here given that this is a shared reset between AHCI and PCIe, should
drivers/reset/reset-brcmstb-rescal.c not implement a .reset() callback
and .assert() callback instead?

>> Otherwise this looks like it'd be missing a reset_control_assert in
>> remove.
> I can add this.
> Thanks,
> Jim
>>
>> regards
>> Philipp

-- 
Florian