linux-kernel - Re: [PATCH] PCI: endpoint: pci-epf-test: Limit PCIe BAR size for fixed BARs

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Message-ID: <99657eb0-e70d-4db3-ac09-6d15c0eb73dd@mailbox.org>
Date: Thu, 4 Sep 2025 19:35:41 +0200
From: Marek Vasut <marek.vasut@...lbox.org>
To: Damien Le Moal <dlemoal@...nel.org>, linux-pci@...r.kernel.org
Cc: Krzysztof Wilczyński <kwilczynski@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Frank Li <Frank.Li@....com>,
 Kishon Vijay Abraham I <kishon@...nel.org>,
 Manivannan Sadhasivam <mani@...nel.org>, Niklas Cassel <cassel@...nel.org>,
 Wang Jiang <jiangwang@...inos.cn>, linux-kernel@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH] PCI: endpoint: pci-epf-test: Limit PCIe BAR size for
 fixed BARs

On 9/4/25 5:39 AM, Damien Le Moal wrote:
> On 9/4/25 12:32 PM, Marek Vasut wrote:
>> On 9/4/25 4:40 AM, Damien Le Moal wrote:
>>
>> Hello Damien,
>>
>>>> @@ -1050,7 +1051,13 @@ static int pci_epf_test_alloc_space(struct pci_epf *epf)
>>>>            if (bar == test_reg_bar)
>>>>                continue;
>>>>    -        base = pci_epf_alloc_space(epf, bar_size[bar], bar,
>>>> +        test_bar_size = bar_size[bar];
>>>> +
>>>> +        bar_fixed_size = epc_features->bar[bar].fixed_size;
>>>> +        if (epc_features->bar[bar].type == BAR_FIXED && bar_fixed_size)
>>>> +            test_bar_size = min(bar_size[bar], bar_fixed_size);
>>>
>>> I think this can be simplified to:
>>>
>>>          if (epc_features->bar[bar].type == BAR_FIXED)
>>>              test_bar_size = epc_features->bar[bar].fixed_size;
>>>          else
>>>              test_bar_size = bar_size[bar];
>>>
>>> because if the bar type is BAR_FIXED, then the size of the bar can only be its
>>> fixed size.
>> That is correct, however, please consider the following case:
>>
>> - The BAR under test is BAR4 , therefore the size requested by this driver is
>> bar_size[4] = 131072 Bytes
>> - The BAR4 on a hypothetical hardware is a fixed size BAR , 262144 Bytes large
>>
>> With your proposed change, the "test_bar_size" would end up being 262144
>> Bytes , instead of 131072 Bytes without your proposed change , which I think is
>> not the desired behavior.
>>
>> What do you think ?
> 
> The bar size for the test is arbitrary. If the bar being tested is not a fixed
> bar, anything is OK. But in the case of a fixed bar, you can only use the fixed
> bar size so we should force that.
OK, understood. I'll run tests on V2 and then submit a V2.

Thanks !