linux-kernel - Re: [PATCH V2] PCI: dwc: Fix n

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Date:   Thu, 29 Sep 2022 10:27:24 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Han Jingoo <jingoohan1@...il.com>
Cc:     gustavo.pimentel@...opsys.com, lpieralisi@...nel.org,
        robh@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        kthota@...dia.com, mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V2] PCI: dwc: Fix n_fts[] array overrun



On 9/29/2022 7:34 AM, Han Jingoo wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Mon, Sep 26, 2022, Vidya Sagar <vidyas@...dia.com> wrote:
>>
>> commit aeaa0bfe89654 ("PCI: dwc: Move N_FTS setup to common setup")
>> incorrectly uses pci->link_gen in deriving the index to the
>> n_fts[] array also introducing the issue of accessing beyond the
>> boundaries of array for greater than Gen-2 speeds. This change fixes
>> that issue.
> 
> Dear Vidya,
> 
> I am just ok with this patch. By the way, do we need another patch to generalize
> this setting? Currently, this code targets only Gen1 and Gen2. But, in
> my opinion,
> it is possible that this driver can be  used for more than Gen2,
> later. PCIe Gen6
> standard is available and Synopsys has their solution for Gen6. So, would you
> send a new patch to generalize this thing, later?
> Thank you.

As I mentioned in the commit message, current code is incorrectly using 
'gen' in the index and ideally n_fts programming has nothing to do with 
the speed and hence I tried to remove the 'gen' reference in the current 
patch. So, the same code (after applying this patch) should work for any 
future Synopsys IP versions supporting higher speeds.

Thanks,
Vidya Sagar

> 
> Best regards,
> Jingoo Han
> 
>>
>> Fixes: aeaa0bfe8965 ("PCI: dwc: Move N_FTS setup to common setup")
>> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
>> Acked-by: Jingoo Han <jingoohan1@...il.com>
>> ---
>> V2:
>> * Addressed review comments from Bjorn
>> * Added "Acked-by: Jingoo Han <jingoohan1@...il.com>"
>>
>>   drivers/pci/controller/dwc/pcie-designware.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
>> index 650a7f22f9d0..3df687667f27 100644
>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>> @@ -649,7 +649,7 @@ void dw_pcie_setup(struct dw_pcie *pci)
>>          if (pci->n_fts[1]) {
>>                  val = dw_pcie_readl_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL);
>>                  val &= ~PORT_LOGIC_N_FTS_MASK;
>> -               val |= pci->n_fts[pci->link_gen - 1];
>> +               val |= pci->n_fts[1];
>>                  dw_pcie_writel_dbi(pci, PCIE_LINK_WIDTH_SPEED_CONTROL, val);
>>          }
>>
>> --
>> 2.17.1
>>