linux-kernel - Re: [PATCH 1/1] PCI: dwc: Fix BAR0 wrong map to iATU6 after root complex reinit endpoint

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Date: Tue, 19 Dec 2023 14:38:34 +0000
From: Niklas Cassel <Niklas.Cassel@....com>
To: Frank Li <Frank.li@....com>
CC: "imx@...ts.linux.dev" <imx@...ts.linux.dev>, Jingoo Han
	<jingoohan1@...il.com>, Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
	Manivannan Sadhasivam <mani@...nel.org>, Lorenzo Pieralisi
	<lpieralisi@...nel.org>, Krzysztof Wilczyński
	<kw@...ux.com>, Rob Herring <robh@...nel.org>, Bjorn Helgaas
	<bhelgaas@...gle.com>, Jon Mason <jdmason@...zu.us>, "open list:PCI DRIVER
 FOR SYNOPSYS DESIGNWARE" <linux-pci@...r.kernel.org>, open list
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] PCI: dwc: Fix BAR0 wrong map to iATU6 after root
 complex reinit endpoint

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@....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@....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.


Kind regards,
Niklas