Re: [PATCH 05/12] PCI: dwc: Set INCREASE_REGION_SIZE flag based on limit address

[Serge Semin <fancer.lancer@gmail.com>]

On Thu, Mar 24, 2022 at 05:35:40PM +0530, Manivannan Sadhasivam wrote:
> On Thu, Mar 24, 2022 at 04:25:16AM +0300, Serge Semin wrote:
> > It was wrong to use the region size parameter in order to determine
> > whether the INCREASE_REGION_SIZE flag needs to be set for the outbound
> > iATU entry because in general there are cases when combining a region base
> > address and size together produces the out of bounds upper range limit
> > while upper_32_bits(size) still returns zero. So having a region size
> > within the permitted values doesn't mean the region limit address will fit
> > to the corresponding CSR. Here is the way iATU calculates the in- and
> > outbound untranslated regions if the INCREASE_REGION_SIZE flag is cleared
> > [1]:
> > 
> >   Start address:                     End address:
> > 63              31              0   63              31              0
> > +---------------+---------------+   +---------------+---------------+
> > |               |         |  0s |   |               |         |  Fs |
> > +---------------+---------------+   +---------------+---------------+
> >    upper base   |   lower base       !upper! base   | limit address
> >      address          address           address
> > 
> > So the region start address is determined by the iATU lower and upper base
> > address registers, while the region upper boundary is calculated based on
> > the 32-bits limit address register and the upper part of the base address.
> > In accordance with that logic for instance the range
> > 0xf0000000 @ 0x20000000 does have the size smaller than 4GB, but the
> > actual limit address turns to be invalid forming the untranslated address
> > map as [0xf0000000; 0x0000FFFF], which isn't what the original range was.
> 

> I find the example confusing:
> 
> If the start address is 0x0-0xf0000000 and size is 0x20000000. Then the end
> address without the INCREASE_REGION_SIZE is going to be:
> 
> 0x0-0x1000FFFF and this is wrong.
> 
> If the INCREASE_REGION_SIZE is set, then the end address will be:
> 
> 0x1-0x1000FFFF and this is correct.

Not only confusing but indeed being wrong in the end address part.
Thanks for noticing that. I'll fix it in v2.

> 
> > In order to fix that we need to check whether the size being added to the
> > lower part of the base address causes the 4GB range overflow. If it does
> > then we need to set the INCREASE_REGION_SIZE flag thus activating the
> > extended limit address by means of an additional iATU CSR (upper limit
> > address register) [2]:
> > 
> >   Start address:                     End address:
> > 63              31              0   63      x       31              0
> > +---------------+---------------+   +---------------+---------------+
> > |               |         |  0s |   |       |       |         |  Fs |
> > +---------------+---------------+   +---------------+---------------+
> >   upper base   |   lower base         upper | upper | limit address
> >     address          address          base  | limit |
> >                                      address|address|
> > 
> > Otherwise there is enough room in the 32-bits wide limit address register,
> > and the flag can be left unset.
> > 
> > Note the case when the size-based flag setting approach is correct implies
> > requiring to have the size-aligned base addresses only. But that
> > restriction isn't relevant to the PCIe ranges accepted by the kernel.
> > There is also no point in implementing it either seeing the problem can be
> > easily fixed by checking the whole limit address instead of the region
> > size.
> > 
> > [1] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
> >     v5.40a, March 2019, fig.3-36, p.175
> > [2] DesignWare Cores PCI Express Controller Databook - DWC PCIe Root Port,
> >     v5.40a, March 2019, fig.3-37, p.176
> > 
> > Fixes: 5b4cf0f65324 ("PCI: dwc: Add upper limit address for outbound iATU")
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> 

> With the example fixed,
> 
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

Ok. Thanks.

-Sergey

> 
> Thanks,
> Mani
> 
> > ---
> >  drivers/pci/controller/dwc/pcie-designware.c | 16 ++++++++++------
> >  1 file changed, 10 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index 7dc8c360a0d4..d737af058903 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -287,8 +287,8 @@ static void dw_pcie_prog_outbound_atu_unroll(struct dw_pcie *pci, u8 func_no,
> >  	dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_UPPER_TARGET,
> >  				 upper_32_bits(pci_addr));
> >  	val = type | PCIE_ATU_FUNC_NUM(func_no);
> > -	val = upper_32_bits(size - 1) ?
> > -		val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > +	if (upper_32_bits(limit_addr) > upper_32_bits(cpu_addr))
> > +		val |= PCIE_ATU_INCREASE_REGION_SIZE;
> >  	if (pci->version == 0x490A)
> >  		val = dw_pcie_enable_ecrc(val);
> >  	dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL1, val);
> > @@ -315,6 +315,7 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> >  					u64 pci_addr, u64 size)
> >  {
> >  	u32 retries, val;
> > +	u64 limit_addr;
> >  
> >  	if (pci->ops && pci->ops->cpu_addr_fixup)
> >  		cpu_addr = pci->ops->cpu_addr_fixup(pci, cpu_addr);
> > @@ -325,6 +326,8 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> >  		return;
> >  	}
> >  
> > +	limit_addr = cpu_addr + size - 1;
> > +
> >  	dw_pcie_writel_dbi(pci, PCIE_ATU_VIEWPORT,
> >  			   PCIE_ATU_REGION_OUTBOUND | index);
> >  	dw_pcie_writel_dbi(pci, PCIE_ATU_LOWER_BASE,
> > @@ -332,17 +335,18 @@ static void __dw_pcie_prog_outbound_atu(struct dw_pcie *pci, u8 func_no,
> >  	dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_BASE,
> >  			   upper_32_bits(cpu_addr));
> >  	dw_pcie_writel_dbi(pci, PCIE_ATU_LIMIT,
> > -			   lower_32_bits(cpu_addr + size - 1));
> > +			   lower_32_bits(limit_addr));
> >  	if (pci->version >= 0x460A)
> >  		dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_LIMIT,
> > -				   upper_32_bits(cpu_addr + size - 1));
> > +				   upper_32_bits(limit_addr));
> >  	dw_pcie_writel_dbi(pci, PCIE_ATU_LOWER_TARGET,
> >  			   lower_32_bits(pci_addr));
> >  	dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> >  			   upper_32_bits(pci_addr));
> >  	val = type | PCIE_ATU_FUNC_NUM(func_no);
> > -	val = ((upper_32_bits(size - 1)) && (pci->version >= 0x460A)) ?
> > -		val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > +	if (upper_32_bits(limit_addr) > upper_32_bits(cpu_addr) &&
> > +	    pci->version >= 0x460A)
> > +		val |= PCIE_ATU_INCREASE_REGION_SIZE;
> >  	if (pci->version == 0x490A)
> >  		val = dw_pcie_enable_ecrc(val);
> >  	dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
> > -- 
> > 2.35.1
> >