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

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Message-ID: <4b8ee973-5201-4936-a248-6f145b958f45@mailbox.org>
Date: Thu, 4 Sep 2025 05:32:15 +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 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 ?