Re: [PATCH v20 09/19] PCI: dwc: Add EDMA_UNROLL capability flag

From: Bjorn Helgaas <helgaas@kernel.org>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: jingoohan1@gmail.com, gustavo.pimentel@synopsys.com,
	lpieralisi@kernel.org, robh+dt@kernel.org, kw@linux.com,
	manivannan.sadhasivam@linaro.org, bhelgaas@google.com,
	kishon@kernel.org, krzysztof.kozlowski+dt@linaro.org,
	conor+dt@kernel.org, marek.vasut+renesas@gmail.com,
	fancer.lancer@gmail.com, linux-pci@vger.kernel.org,
	devicetree@vger.kernel.org, linux-renesas-soc@vger.kernel.org
Subject: Re: [PATCH v20 09/19] PCI: dwc: Add EDMA_UNROLL capability flag
Date: Thu, 14 Sep 2023 11:09:41 -0500	[thread overview]
Message-ID: <20230914160941.GA32484@bhelgaas> (raw)
In-Reply-To: <20230825093219.2685912-10-yoshihiro.shimoda.uh@renesas.com>

On Fri, Aug 25, 2023 at 06:32:09PM +0900, Yoshihiro Shimoda wrote:
> Renesas R-Car Gen4 PCIe controllers have an unexpected register value in
> the eDMA CTRL register. So, add a new capability flag "EDMA_UNROLL"
> which would force the unrolled eDMA mapping for the problematic device.
> 
> Suggested-by: Serge Semin <fancer.lancer@gmail.com>
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 8 +++++++-
>  drivers/pci/controller/dwc/pcie-designware.h | 5 +++--
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index c4998194fe74..4812ce040f1e 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -883,8 +883,14 @@ static int dw_pcie_edma_find_chip(struct dw_pcie *pci)
>  	 * Indirect eDMA CSRs access has been completely removed since v5.40a
>  	 * thus no space is now reserved for the eDMA channels viewport and
>  	 * former DMA CTRL register is no longer fixed to FFs.
> +	 *
> +	 * Note that Renesas R-Car S4-8's PCIe controllers for unknown reason
> +	 * have zeros in the eDMA CTRL register even though the HW-manual
> +	 * explicitly states there must FFs if the unrolled mapping is enabled.
> +	 * For such cases the low-level drivers are supposed to manually
> +	 * activate the unrolled mapping to bypass the auto-detection procedure.
>  	 */
> -	if (dw_pcie_ver_is_ge(pci, 540A))
> +	if (dw_pcie_ver_is_ge(pci, 540A) || dw_pcie_cap_is(pci, EDMA_UNROLL))
>  		val = 0xFFFFFFFF;
>  	else
>  		val = dw_pcie_readl_dbi(pci, PCIE_DMA_VIEWPORT_BASE + PCIE_DMA_CTRL);
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index b731e38a71fc..c7759a508ca9 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -51,8 +51,9 @@
>  
>  /* DWC PCIe controller capabilities */
>  #define DW_PCIE_CAP_REQ_RES		0
> -#define DW_PCIE_CAP_IATU_UNROLL		1
> -#define DW_PCIE_CAP_CDM_CHECK		2
> +#define DW_PCIE_CAP_EDMA_UNROLL		1
> +#define DW_PCIE_CAP_IATU_UNROLL		2
> +#define DW_PCIE_CAP_CDM_CHECK		3

Why did you make the new DW_PCIE_CAP_EDMA_UNROLL "1" and shift all the
existing ones down?  If they don't need to be ordered like this,
leaving the existing ones alone and making DW_PCIE_CAP_EDMA_UNROLL "3"
would be a simpler one-line diff.

>  #define dw_pcie_cap_is(_pci, _cap) \
>  	test_bit(DW_PCIE_CAP_ ## _cap, &(_pci)->caps)
> -- 
> 2.25.1
> 