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

Manivannan Sadhasivam
2022-03-25T06:31:45Z

On Fri, Mar 25, 2022 at 11:57:16AM +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@baikalelectronics.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?
>

Ignore this comment. I failed to notice that your addition.

Thanks,
Mani

> > +
> > #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".
>
> 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
> >