linux-kernel - Re: [PATCH RESEND v4 11/15] PCI: dwc: Simplify in/outbound iATU setup methods

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Date:   Mon, 1 Aug 2022 15:11:53 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Serge Semin <fancer.lancer@...il.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, linux-tegra@...r.kernel.org
Subject: Re: [PATCH RESEND v4 11/15] PCI: dwc: Simplify in/outbound iATU
 setup methods

On Mon, Aug 01, 2022 at 07:20:57PM +0530, Manivannan Sadhasivam wrote:
> On Fri, Jun 24, 2022 at 05:39:43PM +0300, Serge Semin wrote:
> > From maintainability and scalability points of view it has been wrong to
> > use different iATU inbound and outbound regions accessors for the viewport
> > and unrolled versions of the iATU CSRs mapping. Seeing the particular iATU
> > region-wise registers layout is almost fully compatible for different
> > IP-core versions, there were no much points in splitting the code up that
> > way since it was possible to implement a common windows setup methods for
> > both viewport and unrolled iATU CSRs spaces. While what we can observe in
> > the current driver implementation of these methods, is a lot of code
> > duplication, which consequently worsen the code readability,
> > maintainability and scalability. Note the current implementation is a bit
> > more performant than the one suggested in this commit since it implies
> > having less MMIO accesses. But the gain just doesn't worth having the
> > denoted difficulties especially seeing the iATU setup methods are mainly
> > called on the DW PCIe controller and peripheral devices initialization
> > stage.
> > 
> > Here we suggest to move the iATU viewport and unrolled CSR access
> > specifics in the dw_pcie_readl_atu() and dw_pcie_writel_atu() method, and
> > convert the dw_pcie_prog_outbound_atu() and
> > dw_pcie_prog_{ep_}inbound_atu() functions to being generic instead of
> > having a different methods for each viewport and unrolled types of iATU
> > CSRs mapping. Nothing complex really. First of all the dw_pcie_readl_atu()
> > and dw_pcie_writel_atu() are converted to accept relative iATU CSRs
> > address together with the iATU region direction (inbound or outbound) and
> > region index. If DW PCIe controller doesn't have the unrolled iATU CSRs
> > space, then the accessors will need to activate a iATU viewport based on
> > the specified direction and index, otherwise a base address for the
> > corresponding region CSRs will be calculated by means of the
> > PCIE_ATU_UNROLL_BASE() macro. The CSRs macro have been modified in
> > accordance with that logic in the pcie-designware.h header file.
> > 
> > The rest of the changes in this commit just concern converting the iATU
> > in-/out-bound setup methods and iATU regions detection procedure to be
> > compatible with the new accessors semantics. As a result we've dropped the
> > no more required dw_pcie_prog_outbound_atu_unroll(),
> > dw_pcie_prog_inbound_atu_unroll() and dw_pcie_iatu_detect_regions_unroll()
> > methods.
> > 
> > Note aside with the denoted code improvements, there is an additional
> > positive side effect of this change. If at some point an atomic iATU
> > configs setup procedure is required, it will be possible to be done with
> > no much effort just by adding the synchronization into the
> > dw_pcie_readl_atu() and dw_pcie_writel_atu() accessors.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> One nitpick mentioned below. With that fixed,
> 
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

> > +static inline void __iomem *dw_pcie_select_atu(struct dw_pcie *pci, u32 dir,
> 
> This could be renamed to "dw_pcie_get_atu_base()" since we are anyway getting
> the base address of iATU.

I can see it both ways.  It definitely returns a base address, so
"get_atu_base" makes sense.  But it also writes PCIE_ATU_VIEWPORT, and
"select_atu" hints at that side effect while "get_atu_base" does not.

> > +					       u32 index)
> >  {
> > +	void __iomem *base = pci->atu_base;
> > +
> > +	if (pci->iatu_unroll_enabled)
> > +		base += PCIE_ATU_UNROLL_BASE(dir, index);
> > +	else
> > +		dw_pcie_writel_dbi(pci, PCIE_ATU_VIEWPORT, dir | index);
> > +
> > +	return base;
> > +}