Re: [PATCH v5 04/12] PCI: brcmstb: Use bridge reset if available

[James Quinlan <james.quinlan@broadcom.com>]

On 8/12/24 18:28, Stanimir Varbanov wrote:
> Hi Jim,
>
> On 8/12/24 18:46, Jim Quinlan wrote:
>> On Fri, Aug 9, 2024 at 7:16 AM Stanimir Varbanov <svarbanov@suse.de> wrote:
>>> Hi Jim,
>>>
>>> On 8/1/24 01:28, Jim Quinlan wrote:
>>>> The 7712 SOC has a bridge reset which can be described in the device tree.
>>>> Use it if present.  Otherwise, continue to use the legacy method to reset
>>>> the bridge.
>>>>
>>>> Signed-off-by: Jim Quinlan <james.quinlan@broadcom.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 7595e7009192..4d68fe318178 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_reset;
>>>>        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 (val)
>>>> +             reset_control_assert(pcie->bridge_reset);
>>>> +     else
>>>> +             reset_control_deassert(pcie->bridge_reset);
>>>>
>>>> -     tmp = readl(pcie->base + PCIE_RGR1_SW_INIT_1(pcie));
>>>> -     tmp = (tmp & ~mask) | ((val << shift) & mask);
>>>> -     writel(tmp, pcie->base + PCIE_RGR1_SW_INIT_1(pcie));
>>>> +     if (!pcie->bridge_reset) {
>>>> +             u32 tmp, mask =  RGR1_SW_INIT_1_INIT_GENERIC_MASK;
>>>> +             u32 shift = RGR1_SW_INIT_1_INIT_GENERIC_SHIFT;
>>>> +
>>>> +             tmp = readl(pcie->base + PCIE_RGR1_SW_INIT_1(pcie));
>>>> +             tmp = (tmp & ~mask) | ((val << shift) & mask);
>>>> +             writel(tmp, pcie->base + PCIE_RGR1_SW_INIT_1(pcie));
>>>> +     }
>>>>   }
>>>>
>>>>   static void brcm_pcie_bridge_sw_init_set_7278(struct brcm_pcie *pcie, u32 val)
>>>> @@ -1621,10 +1629,16 @@ static int brcm_pcie_probe(struct platform_device *pdev)
>>>>        if (IS_ERR(pcie->perst_reset))
>>>>                return PTR_ERR(pcie->perst_reset);
>>>>
>>>> +     pcie->bridge_reset = devm_reset_control_get_optional_exclusive(&pdev->dev, "bridge");
>>> Shouldn't this be devm_reset_control_get_optional_shared? See more below.
>>>
>>>> +     if (IS_ERR(pcie->bridge_reset))
>>>> +             return PTR_ERR(pcie->bridge_reset);
>>>> +
>>>>        ret = clk_prepare_enable(pcie->clk);
>>>>        if (ret)
>>>>                return dev_err_probe(&pdev->dev, ret, "could not enable clock\n");
>>>>
>>>> +     pcie->bridge_sw_init_set(pcie, 0);
> ^^^ this was missing in v4

Hi Stan,

You are correct and I was remiss in not mentioning this in the cover 
letter.  After my changes on V4 I discovered that my driver failed the 
rebind in my unbind/rebind test and this line was required.

>
>>> According to reset_control_get_shared description looks like this
>>> .deassert is satisfying the requirements for _shared reset-control API
>>> variant.
>>> Is that the intention to call reset_control_deassert() here?
>> Hi Stan,
>> Now I'm not sure I understand you.  All of the resets (bridge, perst,
>> swinit) are exclusive, except for the "rescal" reset, which is shared.
> ... the call of pcie->bridge_sw_init_set(pcie, 0) from brcm_pcie_probe()
> was missing in previous v4 and I'm wondering what changed in v5.
>
> And because of _shared reset-control description [1] I decided (wrongly)
> that the bridge reset could be _shared_.
>
>> On the exclusive resets I am using reset_control_assert() and
>> reset_control_deasssert().  On the shared reset I am using
>> reset_control_rearm() and reset_control_reset().   Why do
>> you think the calls I am using are incongruent with the shard/exclusive
>> status?
> I'd argue that rescal reset is not correctly used in brcm_pcie_probe(),
> see [2] and according to [1] "Calling reset_control_reset is also not
> allowed on a shared reset control."

This is interesting because in reset/core.c [1]  the comment says that 
"reset_control_rearm", which is clearly used for shared resets, must be 
paired with calls to "reset_control_reset".

Regards,

Jim Quinlan

Broadcom STB/CM

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/reset/core.c?h=v6.11-rc3#n412

>
>
> [1]
> https://elixir.bootlin.com/linux/v6.11-rc3/source/include/linux/reset.h#L338
>
> [2]
> https://elixir.bootlin.com/linux/v6.11-rc3/source/drivers/pci/controller/pcie-brcmstb.c#L1632
>
> ~Stan