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

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Message-ID: <20220418071712.ahws4na2bjpbjcsk@mobilestation>
Date:   Mon, 18 Apr 2022 10:17:12 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        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>,
        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 11:33:49AM +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.

Just to be clear. It has only one benefit - an ability to preserve a
device-specific data in the dw_edma_debugfs_entry structure. That data
will be the dw_edma private data instance, which in it turn will be
used to access the register spin lock. All of that in general is
required to support more than one DW eDMA controllers in the system.

> 
> > 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?

Good question. It has just slipped through my fingers in from the
previous code. You are right. I should drop it.

-Sergey

> 
> 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
> >