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Message-ID: <nl4byqs3boe3zke6yvnxmwpgw5oi63ubo36rgzejzg2c4ymwm5@utad76n57gr5>
Date: Tue, 27 Feb 2024 15:21:00 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
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>
Subject: Re: [PATCH v3 2/5] PCI: dwc: Skip finding eDMA channels count if
glue drivers have passed them
On Tue, Feb 27, 2024 at 02:12:04PM +0530, Manivannan Sadhasivam wrote:
> On Tue, Feb 27, 2024 at 12:32:44AM +0300, Serge Semin wrote:
> > On Mon, Feb 26, 2024 at 09:00:14PM +0530, Manivannan Sadhasivam wrote:
> > > On Mon, Feb 26, 2024 at 03:53:20PM +0300, Serge Semin wrote:
> > > > On Mon, Feb 26, 2024 at 05:07:27PM +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 finding the channels if the channels count
> > > > > were already passed by glue drivers. If the channels count passed 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>
> > > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > > > ---
> > > > > drivers/pci/controller/dwc/pcie-designware.c | 16 +++++++++-------
> > > > > 1 file changed, 9 insertions(+), 7 deletions(-)
> > > > >
> > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > index 193fcd86cf93..ce273c3c5421 100644
> > > > > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > > > > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > > > > @@ -927,13 +927,15 @@ 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
> > > > > - val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
> > > > > -
> > > > > - pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
> > > > > - pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
> > > >
> > > > > + if (!pci->edma.ll_wr_cnt || !pci->edma.ll_rd_cnt) {
> > > >
> > > > Are you sure that the partly initialized case should be considered as
> > > > a request for the auto-detection? IMO &&-ing here and letting the
> > > > sanity check to fail further would be more correct since thus the
> > > > developer would know about improper initialized data.
> > > >
> > >
> > > We already have the check below. So the partly initialized case will fail
> > > anyway.
> >
> > Not really. If the partly initialized case activates the
> > auto-detection procedure it will override both non-initialized and
> > _initialized_ number of channels with the values retrieved from the
> > hardware, which the glue driver has been willing not to use. This
> > prone to undefined behavior depending on the reasons of skipping the
> > auto-detection procedure. For instance, assume the DMA_CTRL register
> > reports an invalid number of read channels. A glue driver by mistake
> > or willingly overwrites the pci->edma.ll_rd_cnt field only. This won't
> > solve the problem since the auto-detection will be proceeded due to
> > the pci->edma.ll_wr_cnt field being left uninitialized.
> >
> > So to speak it would be better to implement a strictly determined case
> > for activating the auto-detection procedure: both number of channels
> > aren't initialized; if only one field is initialized then report an
> > error.
> >
> > Alternatively we can have the auto-detection executed on the
> > per-channel basis:
> >
> > + if (pci->edma.mf != EDMA_MF_HDMA_NATIVE) {
> > + val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
> > +
> > + if (!pci->edma.ll_wr_cnt)
> > + pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
> > +
> > + if (!pci->edma.ll_rd_cnt)
> > + pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
> > + }
> >
>
> Hmm, in this case there is no need to check for uninitialized channels count:
>
> /*
> * 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.
> */
> if (pci->edma.mf != EDMA_MF_HDMA_NATIVE) {
> val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
>
> pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
> pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
> }
>
> /* Sanity check */
That is another possible implementation. Let's sum all of them up:
1. Channel fields-base conditional statement:
+ if (!pci->edma.ll_wr_cnt && !pci->edma.ll_rd_cnt) {
+ val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
+
+ pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
+ pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
+ }
pros: NoF channels override support for all IP-cores; simple.
cons: incompatible with HDMA, but can be taken by mistake/bug; no
partial NoF channels pre-initialization.
2. Channel fields-base conditional statement with logical OR operator #1:
+ if (!pci->edma.ll_wr_cnt || !pci->edma.ll_rd_cnt) {
+ val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
+
+ pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
+ pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
+ }
pros: NoF channels override support for all IP-cores; simple.
cons: incompatible with HDMA, but can be taken by mistake/bug; no
partial NoF channels pre-initialization; silently overrides the
partial NoF channels case.
3. Channel fields-base conditional statement with logical OR operator #2:
+ if (!pci->edma.ll_wr_cnt || !pci->edma.ll_rd_cnt) {
+ val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
+
+ if (!pci->edma.ll_wr_cnt)
+ pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
+
+ if (!pci->edma.ll_rd_cnt)
+ pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
+ }
pros: NoF channels override support for all IP-cores; partial NoF
channels pre-initialization support.
cons: incompatible with HDMA, but can be taken by mistake/bug; more
complex (and actually looking a bit clumsy due to two conditional
statements over the same fields).
4. Unconditional auto-detection:
+ val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
+
+ if (!pci->edma.ll_wr_cnt)
+ pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
+
+ if (!pci->edma.ll_rd_cnt)
+ pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
pros: NoF channels override support for all IP-cores; partial NoF
channels pre-initialization support; simple.
cons: incompatible with HDMA, but will be executed for it anyway so
the NoF channels fields will be overridden with the Channel#0.prefetch
CSR data if haven't been pre-initialized;
5. Mapping format-based conditional statement:
+ if (pci->edma.mf != EDMA_MF_HDMA_NATIVE) {
+ val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
+
+ pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
+ pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
+ }
pros: free of being executed for HDMA IP-core, simple
cons: no NoF channels override support for non-HDMA IP-cores.
6. Mapping format-based conditional statement with partial NoF channels override:
+ if (pci->edma.mf != EDMA_MF_HDMA_NATIVE) {
+ val = dw_pcie_readl_dma(pci, PCIE_DMA_CTRL);
+
+ if (!pci->edma.ll_wr_cnt)
+ pci->edma.ll_wr_cnt = FIELD_GET(PCIE_DMA_NUM_WR_CHAN, val);
+
+ if (!pci->edma.ll_rd_cnt)
+ pci->edma.ll_rd_cnt = FIELD_GET(PCIE_DMA_NUM_RD_CHAN, val);
+ }
pros: free of being executed for HDMA IP-core; NoF channels override
support for all IP-cores.
cons: more complex.
Looking at all of that I'd say that options 5 and 6 seems better to me
now since they prohibit the auto-detection for HDMA IP-cores which
have the Channel#0.prefetch CSR at the 0x8 offset. I don't have strong
opinion which of those two to choose. If you think simplicity is
preferable, then option 2 will be enough. If you wish to have the NoF
channels override supported for all IP-cores, then option 3 will work
for it.
-Serge(y)
>
> - Mani
>
> --
> மணிவண்ணன் சதாசிவம்
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