linux-kernel - Re: [PATCH RESEND v5 24/24] PCI: dwc: Add DW eDMA engine support

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Date:   Wed, 24 Aug 2022 11:51:18 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jingoo Han <jingoohan1@...il.com>, Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        linux-pci@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v5 24/24] PCI: dwc: Add DW eDMA engine support

On Mon, Aug 22, 2022 at 09:53:32PM +0300, Serge Semin wrote:
> Since the DW eDMA driver now supports eDMA controllers embedded into the
> locally accessible DW PCIe Root Ports and Endpoints, we can use the
> updated interface to register DW eDMA as DMA engine device if it's
> available. In order to successfully do that the DW PCIe core driver need
> to perform some preparations first. First of all it needs to find out the
> eDMA controller CSRs base address, whether they are accessible over the
> Port Logic or iATU unrolled space. Afterwards it can try to auto-detect
> the eDMA controller availability and number of it's read/write channels.

s/it's//

> If none was found the procedure will just silently halt with no error
> returned. Secondly the platform is supposed to provide either combined or
> per-channel IRQ signals. If no valid IRQs set is found the procedure will
> also halt with no error returned so to be backward compatible with the
> platforms where DW PCIe controllers have eDMA embedded but lack of the
> IRQs defined for them. Finally before actually probing the eDMA device we
> need to allocate LLP items buffers. After that the DW eDMA can be
> registered. If registration is successful the info-message regarding the
> number of detected Read/Write eDMA channels will be printed to the system
> log in the similar way as it's done for the iATU settings.

s/in the similar way as it's done/as is done/

> +static int dw_pcie_edma_find_chip(struct dw_pcie *pci)
> +{
> +	u32 val;
> +
> +	val = dw_pcie_readl_dbi(pci, PCIE_DMA_VIEWPORT_BASE + PCIE_DMA_CTRL);
> +	if (val == 0xFFFFFFFF && pci->edma.reg_base) {
> +		pci->edma.mf = EDMA_MF_EDMA_UNROLL;
> +
> +		val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
> +	} else if (val != 0xFFFFFFFF) {

Consider PCI_POSSIBLE_ERROR() as an annotation about the meaning of
0xFFFFFFFF and something to grep for.

> +		pci->edma.mf = EDMA_MF_EDMA_LEGACY;
> +
> +		pci->edma.reg_base = pci->dbi_base + PCIE_DMA_VIEWPORT_BASE;
> +	} else {
> +		return -ENODEV;
> +	}

> + * eDMA CSRs. DW PCIe IP-core v4.70a and older had the eDMA registers accessible
> + * over the Port Logic registers space. Afterwords the unrolled mapping was

s/Afterwords/Afterwards/

> + * introduced so eDMA and iATU could be accessed via a dedicated registers
> + * space.