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: <20240226153014.GG8422@thinkpad>
Date: Mon, 26 Feb 2024 21:00:14 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Serge Semin <fancer.lancer@...il.com>
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 03:53:20PM +0300, Serge Semin wrote:
> 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.
> 

We already have the check below. So the partly initialized case will fail
anyway.

- Mani

> -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
> > 

-- 
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