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Date: Thu, 29 Feb 2024 13:03:14 +0100
From: Niklas Cassel <cassel@kernel.org>
To: Manivannan Sadhasivam <mani@kernel.org>
Cc: Frank Li <Frank.li@nxp.com>, Niklas Cassel <Niklas.Cassel@wdc.com>,
	"imx@lists.linux.dev" <imx@lists.linux.dev>,
	Jingoo Han <jingoohan1@gmail.com>,
	Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>,
	Rob Herring <robh@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
	Jon Mason <jdmason@kudzu.us>,
	"open list:PCI DRIVER FOR SYNOPSYS DESIGNWARE" <linux-pci@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1] PCI: dwc: Fix BAR0 wrong map to iATU6 after root
 complex reinit endpoint
Message-ID: <ZeBygq5FngE2vlL-@fedora>
References: <20231219044844.1195294-1-Frank.Li@nxp.com>
 <ZYFrUWM7JXdv7rtb@x1-carbon>
 <ZYGmpaf18pJgM/qj@lizhi-Precision-Tower-5810>
 <ZYGq6RdCfdhXFF/9@x1-carbon>
 <ZZ1Pj3MvhQNMnP8M@x1-carbon>
 <ZbFEafUmqmE0nrPx@lizhi-Precision-Tower-5810>
 <20240130062938.GB32821@thinkpad>
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On Tue, Jan 30, 2024 at 11:59:38AM +0530, Manivannan Sadhasivam wrote:
> On Wed, Jan 24, 2024 at 12:10:01PM -0500, Frank Li wrote:
> > On Tue, Jan 09, 2024 at 01:52:15PM +0000, Niklas Cassel wrote:
> > > Hello Frank,
> > > 
> > > On Tue, Dec 19, 2023 at 03:38:33PM +0100, Niklas Cassel wrote:
> > > > On Tue, Dec 19, 2023 at 09:20:21AM -0500, Frank Li wrote:
> > > > > On Tue, Dec 19, 2023 at 10:07:14AM +0000, Niklas Cassel wrote:
> > > > > > On Mon, Dec 18, 2023 at 11:48:43PM -0500, Frank Li wrote:
> > > > > > > dw_pcie_ep_inbound_atu()
> > > > > > > {
> > > > > > > 	...
> > > > > > > 	if (!ep->bar_to_atu[bar])
> > > > > > > 		free_win = find_first_zero_bit(ep->ib_window_map, pci->num_ib_windows);
> > > > > > > 	else
> > > > > > > 		free_win = ep->bar_to_atu[bar];
> > > > > > > 	...
> > > > > > > }
> > > > > > > 
> > > > > > > The atu index 0 is valid case for atu number. The find_first_zero_bit()
> > > > > > > will return 6 when second time call into this function if atu is 0. Suppose
> > > > > > > it should use branch 'free_win = ep->bar_to_atu[bar]'.
> > > > > > > 
> > > > > > > Change 'bar_to_atu' to s8. Initialize bar_to_atu as -1 to indicate it have
> > > > > > > not allocate atu to the bar.
> > > > > > > 
> > > > > > > Reported-by: Niklas Cassel <Niklas.Cassel@wdc.com>
> > > > > > > Close: https://lore.kernel.org/linux-pci/ZXt2A+Fusfz3luQV@x1-carbon/T/#u
> > > > > > > Fixes: 4284c88fff0e ("PCI: designware-ep: Allow pci_epc_set_bar() update inbound map address")
> > > > > > > Signed-off-by: Frank Li <Frank.Li@nxp.com>
> > > > > > > ---
> > > > > > > 
> > > > > > > Notes:
> > > > > > >     @Niklas:
> > > > > > >     	I have not test your case. I should be equal to previous's fix in
> > > > > > >     mail list.
> > > > > > 
> > > > > > Hello Frank,
> > > > > > 
> > > > > > Thank you for sending a proper fix for this!
> > > > > > 
> > > > > > Personally, I slightly prefer your fix that saves the iatu index + 1, and
> > > > > > keeps 0 to mean unused. That way, you don't need the memset, and you don't
> > > > > > need to change the type to signed, but either way is fine by me, so:
> > > > > 
> > > > > index + 1 don't match hardware iATU index. It will be confused because
> > > > > other parts is 0 based.
> > > > > 
> > > > > So I choose "-1" as free iATU.
> > > > 
> > > > A s8 can hold a max value of 127.
> > > > CX_ATU_NUM_OUTBOUND_REGIONS seems to be 0-255.
> > > > 
> > > > Since the DWC code can be synthesized with 256 iATUs,
> > > > your code will not work on systems with 128 or more iATUs.
> > > > 
> > > > If we continue to use a u8, and offset the saved value by one,
> > > > we will at least be able to support 255-1 == 254 iATUs.
> > > 
> > > Do you plan to send out a v2?
> > 
> > @mani:
> > 	Do you have any comments about this fixes except u8's problem?
> 
> IMO, the core issue lies in the EPF driver. It calls set_bar() during init, but
> it is not clearing the BARs with clear_bar() during LINK_DOWN.
> 
> If the BARs were cleared properly, then we would not see this issue.
> 
> I'm planning to do a cleanup of the behavior of EPF with core_init_notifier and
> it should get addressed there.

Hello Mani, Frank,

Please reconsider respinning this.

I think that the invalid usage of find_first_zero_bit() is very bad,
because other people might copy the find_first_zero_bit() usage here.


find_first_zero_bit() can (and will) return 0, so this check is just bad:

if (!ep->bar_to_atu[bar])
        free_win = find_first_zero_bit(ep->ib_window_map, pci->num_ib_windows);

..

ep->bar_to_atu[bar] = free_win;
set_bit(free_win, ep->ib_window_map);


No matter which code Mani adds that cleans up the BARs, will not change that
the logic is this function is just broken.


Kind regards,
Niklas