Message-ID: <20220519074053.GA24064@workstation>
Date:   Thu, 19 May 2022 13:10:53 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Frank Li <Frank.Li@....com>, Rob Herring <robh+dt@...nel.org>,
        linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 15/17] PCI: dwc: Introduce dma-ranges property support
 for RC-host

On Wed, May 18, 2022 at 10:26:23PM +0300, Serge Semin wrote:
> On Tue, May 17, 2022 at 10:50:42PM +0530, Manivannan Sadhasivam wrote:
> > On Thu, May 12, 2022 at 10:41:35PM +0300, Serge Semin wrote:
> > > On Thu, May 12, 2022 at 07:27:08PM +0530, Manivannan Sadhasivam wrote:
> > > > On Wed, May 04, 2022 at 12:46:36AM +0300, Serge Semin wrote:
> > > > > In accordance with the generic PCIe Root Port DT-bindings the "dma-ranges"
> > > > > property has the same format as the "ranges" property. The only difference
> > > > > is in their semantics. The "dma-ranges" property describes the PCIe-to-CPU
> > > > > memory mapping in opposite to the CPU-to-PCIe mapping of the "ranges"
> > > > > property. Even though the DW PCIe controllers are normally equipped with
> > > > > internal Address Translation Unit which inbound and outbound tables can be
> > > > > used to implement both properties semantics, it was surprise for me to
> > > > > discover that the host-related part of the DW PCIe driver currently
> > > > > supports the "ranges" property only while the "dma-ranges" windows are
> > > > > just ignored. Having the "dma-ranges" supported in the driver would be
> > > > > very handy for the platforms, that don't tolerate the 1:1 CPU-PCIe memory
> > > > > mapping and require customized the PCIe memory layout. So let's fix that
> > > > > by introducing the "dma-ranges" property support.
> > > > > 
> > > > > First of all we suggest to rename the dw_pcie_prog_inbound_atu() method to
> > > > > dw_pcie_prog_ep_inbound_atu() and create a new version of the
> > > > > dw_pcie_prog_inbound_atu() function. Thus we'll have two methods for RC
> > > > > and EP controllers respectively in the same way as it has been developed
> > > > > for the outbound ATU setup methods.
> > > > > 
> > > > > Secondly aside with the memory window index and type the new
> > > > > dw_pcie_prog_inbound_atu() function will accept CPU address, PCIe address
> > > > > and size as its arguments. These parameters define the PCIe and CPU memory
> > > > > ranges which will be used to setup the respective inbound ATU mapping. The
> > > > > passed parameters need to be verified against the ATU ranges constraints
> > > > > in the same way as it is done for the outbound ranges.
> > > > > 
> > > > > Finally the DMA-ranges detected for the PCIe controller need to be
> > > > > converted into the inbound ATU entries during the host controller
> > > > > initialization procedure. It will be done in the framework of the
> > > > > dw_pcie_iatu_setup() method. Note before setting the inbound ranges up we
> > > > > need to disable all the inbound ATU entries in order to prevent unexpected
> > > > > PCIe TLPs translations defined by some third party software like
> > > > > bootloader.
> > > > > 
> > > > > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > > > > ---
> > > > >  .../pci/controller/dwc/pcie-designware-ep.c   |  4 +-
> > > > >  .../pci/controller/dwc/pcie-designware-host.c | 32 ++++++++++-
> > > > >  drivers/pci/controller/dwc/pcie-designware.c  | 57 ++++++++++++++++++-
> > > > >  drivers/pci/controller/dwc/pcie-designware.h  |  6 +-
> > > > >  4 files changed, 90 insertions(+), 9 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > > index c62640201246..9b0540cfa9e8 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > > > @@ -167,8 +167,8 @@ static int dw_pcie_ep_inbound_atu(struct dw_pcie_ep *ep, u8 func_no, int type,
> > > > >  		return -EINVAL;
> > > > >  	}
> > > > >  
> > > > > -	ret = dw_pcie_prog_inbound_atu(pci, func_no, free_win, type,
> > > > > -				       cpu_addr, bar);
> > > > > +	ret = dw_pcie_prog_ep_inbound_atu(pci, func_no, free_win, type,
> > > > > +					  cpu_addr, bar);
> > > > >  	if (ret < 0) {
> > > > >  		dev_err(pci->dev, "Failed to program IB window\n");
> > > > >  		return ret;
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > > > index 7caca6c575a5..9cb406f5c185 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > > > @@ -612,12 +612,15 @@ static int dw_pcie_iatu_setup(struct pcie_port *pp)
> > > > >  	}
> > > > >  
> > > > >  	/*
> > > > > -	 * Ensure all outbound windows are disabled before proceeding with
> > > > > -	 * the MEM/IO ranges setups.
> > > > > +	 * Ensure all out/inbound windows are disabled before proceeding with
> > > > > +	 * the MEM/IO (dma-)ranges setups.
> > > > >  	 */
> > > > >  	for (i = 0; i < pci->num_ob_windows; i++)
> > > > >  		dw_pcie_disable_atu(pci, PCIE_ATU_REGION_DIR_OB, i);
> > > > >  
> > > > > +	for (i = 0; i < pci->num_ib_windows; i++)
> > > > > +		dw_pcie_disable_atu(pci, PCIE_ATU_REGION_DIR_IB, i);
> > > > > +
> > > > >  	i = 0;
> > > > >  	resource_list_for_each_entry(entry, &pp->bridge->windows) {
> > > > >  		if (resource_type(entry->res) != IORESOURCE_MEM)
> > > > > @@ -654,9 +657,32 @@ static int dw_pcie_iatu_setup(struct pcie_port *pp)
> > > > >  	}
> > > > >  
> > > > >  	if (pci->num_ob_windows <= i)
> > > > > -		dev_warn(pci->dev, "Resources exceed number of ATU entries (%d)\n",
> > > > > +		dev_warn(pci->dev, "Ranges exceed outbound iATU size (%d)\n",
> > > > >  			 pci->num_ob_windows);
> > > > >  
> > > > > +	i = 0;
> > > > > +	resource_list_for_each_entry(entry, &pp->bridge->dma_ranges) {
> > > > > +		if (resource_type(entry->res) != IORESOURCE_MEM)
> > > > > +			continue;
> > > > > +
> > > > > +		if (pci->num_ib_windows <= i)
> > > > > +			break;
> > > > > +
> > > > > +		ret = dw_pcie_prog_inbound_atu(pci, i++, PCIE_ATU_TYPE_MEM,
> > > > > +					       entry->res->start,
> > > > > +					       entry->res->start - entry->offset,
> > > > > +					       resource_size(entry->res));
> > > > > +		if (ret) {
> > > > > +			dev_err(pci->dev, "Failed to set DMA range %pr\n",
> > > > > +				entry->res);
> > > > > +			return ret;
> > > > > +		}
> > > > > +	}
> > > > > +
> > > > > +	if (pci->num_ib_windows <= i)
> > > > > +		dev_warn(pci->dev, "Dma-ranges exceed inbound iATU size (%u)\n",
> > > > > +			 pci->num_ib_windows);
> > > > > +
> > > > >  	return 0;
> > > > >  }
> > > > >  
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > index 747e252c09e6..33718ed6c511 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > @@ -397,8 +397,61 @@ static inline void dw_pcie_writel_atu_ib(struct dw_pcie *pci, u32 index, u32 reg
> > > > >  	dw_pcie_writel_atu(pci, PCIE_ATU_REGION_DIR_IB, index, reg, val);
> > > > >  }
> > > > >  
> > > > > -int dw_pcie_prog_inbound_atu(struct dw_pcie *pci, u8 func_no, int index,
> > > > > -			     int type, u64 cpu_addr, u8 bar)
> > > > > +int dw_pcie_prog_inbound_atu(struct dw_pcie *pci, int index, int type,
> > > > > +			     u64 cpu_addr, u64 pci_addr, u64 size)
> > > > > +{
> > > > > +	u64 limit_addr = pci_addr + size - 1;
> > > > > +	u32 retries, val;
> > > > > +
> > > > > +	if ((limit_addr & ~pci->region_limit) != (pci_addr & ~pci->region_limit) ||
> > > > > +	    !IS_ALIGNED(cpu_addr, pci->region_align) ||
> > > > > +	    !IS_ALIGNED(pci_addr, pci->region_align) ||
> > > > > +	    !IS_ALIGNED(size, pci->region_align) ||
> > > > 
> > > 
> > > > Why do you want the size to be aligned? What if I want to transfer a small size
> > > > buffer?
> > > > 
> > > > Same question applies to outbound programming as well.
> > > 
> > > You can't program a region with the unaligned size by the DW PCIe CSRs
> > > design. The limit address lower bits are read-only and fixed with
> > > one's in accordance with the IP-core synthesize parameter
> > > CX_ATU_MIN_REGION_SIZE. So the mapping is always performed in the
> > > CX_ATU_MIN_REGION_SIZE chunks.
> > > 
> > > IATU_LIMIT_ADDR_OFF_{IN,OUT}BOUND.LIMIT_ADDR_HW = 
> > > {(CX_ATU_MIN_REGION_SIZE == 65536) ? "0xffff" :
> > >  (CX_ATU_MIN_REGION_SIZE == 32768) ? "0x7fff" :
> > >  (CX_ATU_MIN_REGION_SIZE == 16384) ? "0x3fff" :
> > >  (CX_ATU_MIN_REGION_SIZE == 8192)  ? "0x1fff" :
> > >  (CX_ATU_MIN_REGION_SIZE == 4096)  ? "0xfff" : "0xffff"}
> > > 
> > 
> 
> > Right. Even though the minimum size that could be mapped is 4k, I could still
> > use that 4k size for mapping small buffers also. So you should not be erroring
> > out here if the size is not aligned. 
> 
> Why would you need to do that? Even if you do and the operation
> doesn't return an error (or at least splash the syslog with a
> warning), the hardware would expand the mapping up to the aligned size
> anyway. Such implicit behavior would have given your software an
> impression that the mapping was performed in the way you asked with
> the size you specified so the upper part of the unaligned range is
> free to be used for something else. If the range is accessed, instead
> of a bus error or silent IO termination it may cause unexpected result
> of creating random PCIe bus traffic. So I'd rather have the
> code/platform setup fixed right from the start instead of waiting for
> the hard to find bug cause.
> 

The application I'm working on is MHI bus. As per the design, it needs to copy
16byte data to ring buffers in the host memory. If I use iATU, then I
cannot copy those small data with the size alignment.

> > I know that it is a waste of memory but that doesn't mean that it won't work.
> 
> The correct statement in this case would be "it won't work in a way
> you expected, but with the implicit side effect applied to the memory
> above the requested one."
> 

Agree but that would only happen when the application does out of bound
access and in that case the issue is with the application.

Thanks,
Mani

> -Sergey
> 
> > 
> > Thanks,
> > Mani
> > 
> > > -Sergey
> > > 
> > > > 
> > > > Thanks,
> > > > Mani
> > > > 
> > > > -- 
> > > > மணிவண்ணன் சதாசிவம்
> > 
> > -- 
> > மணிவண்ணன் சதாசிவம்

Powered by blists - more mailing lists