linux-kernel - Re: [PATCH 16/25] dmaengine: dw-edma: Simplify the DebugFS context CSRs init procedure

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Date:   Mon, 18 Apr 2022 11:23:45 +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 16/25] dmaengine: dw-edma: Simplify the DebugFS context
 CSRs init procedure

On Fri, Mar 25, 2022 at 11:57:08AM +0530, Manivannan Sadhasivam wrote:
> On Thu, Mar 24, 2022 at 04:48:27AM +0300, Serge Semin wrote:
> > DW eDMA v4.70a and older have the read and write channels context CSRs
> > indirectly accessible. It means the CSRs like Channel Control, Xfer size,
> > SAR, DAR and LLP address are accessed over at a fixed MMIO address, but
> > their reference to the corresponding channel is determined by the Viewport
> > CSR. In order to have a coherent access to these registers the CSR IOs are
> > supposed to be protected with a spin-lock. DW eDMA v4.80a and newer
> > normally have unrolled Read/Write channel context registers. That is all
> > CSRs denoted before are directly mapped in the controller MMIO space.
> > 
> > Since both normal and viewport-based registers are exposed via the DebugFS
> > nodes, the original code author decided to implement an algorithm based on
> > the unrolled CSRs mapping with the viewport addresses recalculation if
> > it's required. The problem is that such implementation turned to be first
> > unscalable (supports a platform with only single eDMA available since a
> > base address statically preserved) and second needlessly overcomplicated
> > (it loops over all Rd/Wr context addresses and re-calculates the viewport
> > base address on each DebugFS node access). The algorithm can be greatly
> > simplified just by adding the channel ID and it's direction fields in the
> > eDMA DebugFS node descriptor. These new parameters can be used to find a
> > CSR offset within the corresponding channel registers space. The DW eDMA
> > DebugFS node getter afterwards will also use them in order to activate the
> > respective context CSRs viewport before reading data from the specified
> > register. In case of the unrolled version of the CSRs mapping there won't
> > be any spin-lock taken/released, no viewport activation as before this
> > modification.
> > 
> > Note this modification fixes the REGISTER() macros using an externally
> > defined local variable. The same problem with the rest of the macro will
> > be fixed in the next commit.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> > ---
> >  drivers/dma/dw-edma/dw-edma-v0-debugfs.c | 84 +++++++++++-------------
> >  1 file changed, 38 insertions(+), 46 deletions(-)
> > 
> > diff --git a/drivers/dma/dw-edma/dw-edma-v0-debugfs.c b/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> > index 7eb0147912fa..b34a68964232 100644
> > --- a/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> > +++ b/drivers/dma/dw-edma/dw-edma-v0-debugfs.c
> > @@ -15,9 +15,27 @@
> >  
> >  #define REGS_ADDR(name) \
> >  	((void __iomem *)&regs->name)
> > +
> > +#define REGS_CH_ADDR(name, _dir, _ch)						\
> > +	({									\
> > +		struct dw_edma_v0_ch_regs __iomem *__ch_regs;			\
> > +										\
> > +		if ((dw)->chip->mf == EDMA_MF_EDMA_LEGACY)			\
> > +			__ch_regs = &regs->type.legacy.ch;			\
> > +		else if (_dir == EDMA_DIR_READ)					\
> > +			__ch_regs = &regs->type.unroll.ch[_ch].rd;		\
> > +		else								\
> > +			__ch_regs = &regs->type.unroll.ch[_ch].wr;		\
> > +										\
> > +		(void __iomem *)&__ch_regs->name;				\
> > +	})
> > +
> >  #define REGISTER(name) \
> >  	{ #name, REGS_ADDR(name) }
> >  
> > +#define CTX_REGISTER(name, dir, ch) \
> > +	{ #name, REGS_CH_ADDR(name, dir, ch), dir, ch }
> 
> What is the need of "dir, ch" at the end?
> 
> > +
> >  #define WR_REGISTER(name) \
> >  	{ #name, REGS_ADDR(wr_##name) }
> >  #define RD_REGISTER(name) \
> > @@ -41,14 +59,11 @@
> >  static struct dw_edma				*dw;
> >  static struct dw_edma_v0_regs			__iomem *regs;
> >  
> > -static struct {
> > -	void					__iomem *start;
> > -	void					__iomem *end;
> > -} lim[2][EDMA_V0_MAX_NR_CH];
> > -
> >  struct dw_edma_debugfs_entry {
> >  	const char				*name;
> >  	void __iomem				*reg;
> > +	enum dw_edma_dir			dir;
> > +	u16					ch;
> >  };
> >  
> >  static int dw_edma_debugfs_u32_get(void *data, u64 *val)
> > @@ -58,33 +73,16 @@ static int dw_edma_debugfs_u32_get(void *data, u64 *val)
> >  
> >  	if (dw->chip->mf == EDMA_MF_EDMA_LEGACY &&
> >  	    reg >= (void __iomem *)&regs->type.legacy.ch) {
> > -		void __iomem *ptr = &regs->type.legacy.ch;
> > -		u32 viewport_sel = 0;
> >  		unsigned long flags;
> > -		u16 ch;
> > -
> > -		for (ch = 0; ch < dw->wr_ch_cnt; ch++)
> > -			if (lim[0][ch].start >= reg && reg < lim[0][ch].end) {
> > -				ptr += (reg - lim[0][ch].start);
> > -				goto legacy_sel_wr;
> > -			}
> > -
> > -		for (ch = 0; ch < dw->rd_ch_cnt; ch++)
> > -			if (lim[1][ch].start >= reg && reg < lim[1][ch].end) {
> > -				ptr += (reg - lim[1][ch].start);
> > -				goto legacy_sel_rd;
> > -			}
> > -
> > -		return 0;
> > -legacy_sel_rd:
> > -		viewport_sel = BIT(31);
> > -legacy_sel_wr:
> > -		viewport_sel |= FIELD_PREP(EDMA_V0_VIEWPORT_MASK, ch);
> > +		u32 viewport_sel;
> > +
> > +		viewport_sel = entry->dir == EDMA_DIR_READ ? BIT(31) : 0;
> > +		viewport_sel |= FIELD_PREP(EDMA_V0_VIEWPORT_MASK, entry->ch);
> >  
> >  		raw_spin_lock_irqsave(&dw->lock, flags);
> >  
> >  		writel(viewport_sel, &regs->type.legacy.viewport_sel);
> > -		*val = readl(ptr);
> > +		*val = readl(reg);
> >  
> >  		raw_spin_unlock_irqrestore(&dw->lock, flags);
> >  	} else {
> > @@ -114,19 +112,19 @@ static void dw_edma_debugfs_create_x32(const struct dw_edma_debugfs_entry ini[],
> >  	}
> >  }
> >  
> > -static void dw_edma_debugfs_regs_ch(struct dw_edma_v0_ch_regs __iomem *regs,
> > +static void dw_edma_debugfs_regs_ch(enum dw_edma_dir edma_dir, u16 ch,
> >  				    struct dentry *dir)
> 

> Using "dir" for directory would be confusing since it could also refer
> direction. I'd suggest to use "dentry".

Agreed, but for the sake of consistency this needs to be done for the
whole file. Due to that in some context using "dentry" isn't that
suitable since makes the variables name a bit too long. I'll use
'dent' instead. The change will be submitted as a separate patch in
this series.

-Sergey

> 
> Thanks,
> Mani
> 
> >  {
> > -	const struct dw_edma_debugfs_entry debugfs_regs[] = {
> > -		REGISTER(ch_control1),
> > -		REGISTER(ch_control2),
> > -		REGISTER(transfer_size),
> > -		REGISTER(sar.lsb),
> > -		REGISTER(sar.msb),
> > -		REGISTER(dar.lsb),
> > -		REGISTER(dar.msb),
> > -		REGISTER(llp.lsb),
> > -		REGISTER(llp.msb),
> > +	struct dw_edma_debugfs_entry debugfs_regs[] = {
> > +		CTX_REGISTER(ch_control1, edma_dir, ch),
> > +		CTX_REGISTER(ch_control2, edma_dir, ch),
> > +		CTX_REGISTER(transfer_size, edma_dir, ch),
> > +		CTX_REGISTER(sar.lsb, edma_dir, ch),
> > +		CTX_REGISTER(sar.msb, edma_dir, ch),
> > +		CTX_REGISTER(dar.lsb, edma_dir, ch),
> > +		CTX_REGISTER(dar.msb, edma_dir, ch),
> > +		CTX_REGISTER(llp.lsb, edma_dir, ch),
> > +		CTX_REGISTER(llp.msb, edma_dir, ch),
> >  	};
> >  	int nr_entries;
> >  
> > @@ -191,10 +189,7 @@ static void dw_edma_debugfs_regs_wr(struct dentry *dir)
> >  
> >  		ch_dir = debugfs_create_dir(name, regs_dir);
> >  
> > -		dw_edma_debugfs_regs_ch(&regs->type.unroll.ch[i].wr, ch_dir);
> > -
> > -		lim[0][i].start = &regs->type.unroll.ch[i].wr;
> > -		lim[0][i].end = &regs->type.unroll.ch[i].padding_1[0];
> > +		dw_edma_debugfs_regs_ch(EDMA_DIR_WRITE, i, ch_dir);
> >  	}
> >  }
> >  
> > @@ -256,10 +251,7 @@ static void dw_edma_debugfs_regs_rd(struct dentry *dir)
> >  
> >  		ch_dir = debugfs_create_dir(name, regs_dir);
> >  
> > -		dw_edma_debugfs_regs_ch(&regs->type.unroll.ch[i].rd, ch_dir);
> > -
> > -		lim[1][i].start = &regs->type.unroll.ch[i].rd;
> > -		lim[1][i].end = &regs->type.unroll.ch[i].padding_2[0];
> > +		dw_edma_debugfs_regs_ch(EDMA_DIR_READ, i, ch_dir);
> >  	}
> >  }
> >  
> > -- 
> > 2.35.1
> >