linux-kernel - Re: [PATCH v4 2/5] PCI: dwc: Skip finding eDMA channels count for HDMA platforms

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Date: Mon, 18 Mar 2024 11:04:36 +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>,
	Frank Li <Frank.Li@....com>
Subject: Re: [PATCH v4 2/5] PCI: dwc: Skip finding eDMA channels count for
 HDMA platforms

On Tue, Mar 12, 2024 at 12:17:48PM +0300, Serge Semin wrote:
> On Wed, Mar 06, 2024 at 03:51:58PM +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 the existing auto detection of channels
> > count procedure for HDMA based platforms. If the channels count passed by
> > the glue drivers 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>
> > Reviewed-by: Frank Li <Frank.Li@....com>
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> 
> Reviewed-by: Serge Semin <fancer.lancer@...il.com>
> 
> Please find a tiny nitpick further below.
> 
> > ---
> >  drivers/pci/controller/dwc/pcie-designware.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index 3a26dfc5368f..599991b7ffb2 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -927,13 +927,18 @@ 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
> 
> > +	/*
> > +	 * Autodetect the read/write channels count only for non-HDMA platforms.
> > +	 * HDMA platforms doesn't support autodetect, so the glue drivers should've
> > +	 * passed the valid count already. If not, the below sanity check will
> > +	 * catch it.
> > +	 */
> 
> This is correct for the _native_ HDMA CSRs mapping. I suggest to emphasize
> that in the note above.
> 

Ack.

- Mani

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