linux-kernel - Re: [PATCH v1 3/8] PCI: brcmstb: Use bridge reset if available

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Message-ID: <055fe06c-58c3-42ad-a33e-c39de21f59b1@suse.de>
Date: Wed, 3 Jul 2024 16:09:46 +0300
From: Stanimir Varbanov <svarbanov@...e.de>
To: Jim Quinlan <james.quinlan@...adcom.com>,
 Stanimir Varbanov <svarbanov@...e.de>
Cc: linux-pci@...r.kernel.org, Nicolas Saenz Julienne <nsaenz@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
 Cyril Brulebois <kibi@...ian.org>, bcm-kernel-feedback-list@...adcom.com,
 jim2101024@...il.com, Florian Fainelli <florian.fainelli@...adcom.com>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Rob Herring <robh@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>,
 "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 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/8] PCI: brcmstb: Use bridge reset if available

Hi Jim,

On 7/2/24 21:36, Jim Quinlan wrote:
> On Tue, Jul 2, 2024 at 8:59 AM Stanimir Varbanov <svarbanov@...e.de> wrote:
>>
>>
>>
>> On 6/28/24 23:54, Jim Quinlan wrote:
>>> The 7712 SOC has a bridge reset which can be described in the device tree.
>>> If it is present, use it. Otherwise, continue to use the legacy method to
>>> reset the bridge.
>>>
>>> Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
>>> ---
>>>  drivers/pci/controller/pcie-brcmstb.c | 24 +++++++++++++++++++-----
>>>  1 file changed, 19 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
>>> index c2eb29b886f7..4104c3668fdb 100644
>>> --- a/drivers/pci/controller/pcie-brcmstb.c
>>> +++ b/drivers/pci/controller/pcie-brcmstb.c
>>> @@ -265,6 +265,7 @@ struct brcm_pcie {
>>>       enum pcie_type          type;
>>>       struct reset_control    *rescal;
>>>       struct reset_control    *perst_reset;
>>> +     struct reset_control    *bridge;
>>>       int                     num_memc;
>>>       u64                     memc_size[PCIE_BRCM_MAX_MEMC];
>>>       u32                     hw_rev;
>>> @@ -732,12 +733,19 @@ static void __iomem *brcm7425_pcie_map_bus(struct pci_bus *bus,
>>>
>>>  static void brcm_pcie_bridge_sw_init_set_generic(struct brcm_pcie *pcie, u32 val)
>>>  {
>>> -     u32 tmp, mask =  RGR1_SW_INIT_1_INIT_GENERIC_MASK;
>>> -     u32 shift = RGR1_SW_INIT_1_INIT_GENERIC_SHIFT;
>>> +     if (pcie->bridge) {
>>> +             if (val)
>>> +                     reset_control_assert(pcie->bridge);
>>> +             else
>>> +                     reset_control_deassert(pcie->bridge);
>>
>> Please check reset_control_assert/deassert() calls for error. This might
>> need to change the definition of brcm_pcie_bridge_sw_init_set_generic()
>> to return error.
> 
> Hi Stan,
> 
> Do you really think this is necessary?  If you look at
> "drivers/reset/reset-brcmstb.c"  there is no way for either of these
> calls to fail and I don't see that changing because it is just writing
> a bit into a register.

yes, I think there are kernel rules which we have to follow. We use
generic reset-control interface in pcie driver and we cannot rely on the
low-level implementation of this particular reset-controller driver
(reset-brcmstb.c).

regards,
~Stan