linux-kernel - Re: [PATCH 15/25] dmaengine: dw-edma: Convert DebugFS descs to being kz-allocated

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Message-ID: <20220325064209.GE4675@thinkpad>
Date:   Fri, 25 Mar 2022 12:12:09 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Vinod Koul <vkoul@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Frank Li <Frank.Li@....com>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-pci@...r.kernel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/25] dmaengine: dw-edma: Convert DebugFS descs to being
 kz-allocated

On Fri, Mar 25, 2022 at 11:33:57AM +0530, Manivannan Sadhasivam wrote:
> On Thu, Mar 24, 2022 at 04:48:26AM +0300, Serge Semin wrote:
> > Currently all the DW eDMA DebugFS nodes descriptors are allocated on
> > stack, while the DW eDMA driver private data and CSR limits are statically
> > preserved. Such design won't work for the multi-eDMA platforms.
> 
> Can you please explain why?
> 
> > As a
> > preparation to adding the multi-eDMA system setups support we need to have
> > each DebugFS node separately allocated and described. Afterwards we'll put
> > an addition info there like Read/Write channel flag, channel ID, DW eDMA
> > private data reference.
> > 
> > Note this conversion is mainly required due to having the legacy DW eDMA
> > controllers with indirect Read/Write channels context CSRs access. If we
> > didn't need to have a synchronized access to these registers the DebugFS
> > code of the driver would have been much simpler.
> > 
> 
> I fail to understand how this change is beneficial or the exact issue.
> 

I think I get the reasoning after going through the successive patches.

Thanks,
Mani

> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > ---
> >  drivers/dma/dw-edma/dw-edma-v0-debugfs.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/dma/dw-edma/dw-edma-v0-debugfs.c b/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> > index afd519d9568b..7eb0147912fa 100644
> > --- a/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> > +++ b/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> > @@ -53,7 +53,8 @@ struct dw_edma_debugfs_entry {
> >  
> >  static int dw_edma_debugfs_u32_get(void *data, u64 *val)
> >  {
> > -	void __iomem *reg = data;
> > +	struct dw_edma_debugfs_entry __iomem *entry = data;
> 
> Why the entry has to be of __iomem?
> 
> Thanks,
> Mani
> 
> > +	void __iomem *reg = entry->reg;
> >  
> >  	if (dw->chip->mf == EDMA_MF_EDMA_LEGACY &&
> >  	    reg >= (void __iomem *)&regs->type.legacy.ch) {
> > @@ -94,14 +95,22 @@ static int dw_edma_debugfs_u32_get(void *data, u64 *val)
> >  }
> >  DEFINE_DEBUGFS_ATTRIBUTE(fops_x32, dw_edma_debugfs_u32_get, NULL, "0x%08llx\n");
> >  
> > -static void dw_edma_debugfs_create_x32(const struct dw_edma_debugfs_entry entries[],
> > +static void dw_edma_debugfs_create_x32(const struct dw_edma_debugfs_entry ini[],
> >  				       int nr_entries, struct dentry *dir)
> >  {
> > +	struct dw_edma_debugfs_entry *entries;
> >  	int i;
> >  
> > +	entries = devm_kcalloc(dw->chip->dev, nr_entries, sizeof(*entries),
> > +			       GFP_KERNEL);
> > +	if (!entries)
> > +		return;
> > +
> >  	for (i = 0; i < nr_entries; i++) {
> > +		entries[i] = ini[i];
> > +
> >  		debugfs_create_file_unsafe(entries[i].name, 0444, dir,
> > -					   entries[i].reg, &fops_x32);
> > +					   &entries[i], &fops_x32);
> >  	}
> >  }
> >  
> > -- 
> > 2.35.1
> >