linux-kernel - Re: [PATCH v3 2/5] PCI: dwc: Skip finding eDMA channels count if glue drivers have passed them

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Message-ID: <5gzkxdpx6u3jhw5twbncjhtozgekmlzxrpj3m6is3ijadm2svb@f6ng4owyakup>
Date: Mon, 26 Feb 2024 15:53:20 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Jingoo Han <jingoohan1@...il.com>, 
	Gustavo Pimentel <gustavo.pimentel@...opsys.com>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Krzysztof Wilczyński <kw@...ux.com>, Rob Herring <robh@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Marek Vasut <marek.vasut+renesas@...il.com>, 
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, Kishon Vijay Abraham I <kishon@...nel.org>, 
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, mhi@...ts.linux.dev, Siddharth Vadapalli <s-vadapalli@...com>
Subject: Re: [PATCH v3 2/5] PCI: dwc: Skip finding eDMA channels count if
 glue drivers have passed them

On Mon, Feb 26, 2024 at 05:07:27PM +0530, Manivannan Sadhasivam wrote:
> In the case of Hyper DMA (HDMA) present in DWC controllers, there is no way
> the drivers can auto detect the number of read/write channels as like its
> predecessor embedded DMA (eDMA). So the glue drivers making use of HDMA
> have to pass the channels count during probe.
> 
> To accommodate that, let's skip finding the channels if the channels count
> were already passed by glue drivers. If the channels count passed were
> wrong in any form, then the existing sanity check will catch it.
> 
> Suggested-by: Serge Semin <fancer.lancer@...il.com>
> Reviewed-by: Siddharth Vadapalli <s-vadapalli@...com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-designware.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> index 193fcd86cf93..ce273c3c5421 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.c
> +++ b/drivers/pci/controller/dwc/pcie-designware.c
> @@ -927,13 +927,15 @@ static int dw_pcie_edma_find_channels(struct dw_pcie *pci)
>  {
>  	u32 val;
>  
> -	if (pci->edma.mf == EDMA_MF_EDMA_LEGACY)
> -		val = dw_pcie_readl_dbi(pci, PCIE_DMA_VIEWPORT_BASE + PCIE_DMA_CTRL);
> -	else
> -		val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
> -
> -	pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
> -	pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);

> +	if (!pci->edma.ll_wr_cnt || !pci->edma.ll_rd_cnt) {

Are you sure that the partly initialized case should be considered as
a request for the auto-detection? IMO &&-ing here and letting the
sanity check to fail further would be more correct since thus the
developer would know about improper initialized data.

-Serge(y)

> +		if (pci->edma.mf == EDMA_MF_EDMA_LEGACY)
> +			val = dw_pcie_readl_dbi(pci, PCIE_DMA_VIEWPORT_BASE + PCIE_DMA_CTRL);
> +		else
> +			val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
> +
> +		pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
> +		pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
> +	}
>  
>  	/* Sanity check the channels count if the mapping was incorrect */
>  	if (!pci->edma.ll_wr_cnt || pci->edma.ll_wr_cnt > EDMA_MAX_WR_CH ||
> 
> -- 
> 2.25.1
>