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Tue, 21 Jan 2025 09:09:48 -0800 (PST) Date: Tue, 21 Jan 2025 18:09:43 +0100 From: Stephan Gerhold To: Md Sadre Alam Cc: vkoul@kernel.org, kees@kernel.org, fenghua.yu@intel.com, linux-arm-msm@vger.kernel.org, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, djakov@kernel.org, quic_srichara@quicinc.com, quic_varada@quicinc.com Subject: Re: [PATCH v3] dmaengine: qcom: bam_dma: Fix BAM_RIVISON register handling Message-ID: References: <20250121091241.2646532-1-quic_mdalam@quicinc.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250121091241.2646532-1-quic_mdalam@quicinc.com> On Tue, Jan 21, 2025 at 02:42:41PM +0530, Md Sadre Alam wrote: > This patch resolves a bug from the previous commit where the > BAM_DESC_CNT_TRSHLD register was conditionally written based on BAM-NDP > mode. The issue was reading the BAM_REVISION register hanging if num-ees > was not zero, which occurs when the SoCs power on BAM remotely. So the > BAM_REVISION register read has been moved to inside if condition. > > Fixes: 57a7138d0627 ("dmaengine: qcom: bam_dma: Avoid writing unavailable register") > Reported-by: Georgi Djakov > Link: https://lore.kernel.org/lkml/9ef3daa8-cdb1-49f2-8d19-a72d6210ff3a@kernel.org/ > Signed-off-by: Md Sadre Alam I'm afraid there are still two open problems here: 1. In your original commit, you added the if (in_range(...)) checks to make the BAM_DESC_CNT_TRSHLD register write conditional. With this patch we only read the bam_revision for the !bdev->num_ees case. This means that even if we have e.g. a remotely powered BAM-NDP, we don't initialize BAM_DESC_CNT_TRSHLD anymore. 2. Aside from BAM-NDP and BAM-Lite there is also plain "BAM". You mentioned we should only skip the register write for BAM-Lite, but the plain "BAM" isn't handled anywhere yet. I would recommend inverting the in_range(...) checks to check for if (!in_range(BAM-LITE) rather than if (in_range(BAM-NDP)). This should also work for the plain "BAM" type. It will also avoid regressions if we don't read the bam_revision in the !bdev->num_ees case. (Although ideally you would lazily initialize the bam_revision to cover all the configurations.) Thanks, Stephan > --- > > Change in [v3] > > * Revised commit details > > Change in [v2] > > * Removed unnecessary if checks. > * Relocated the BAM_REVISION register read within the if condition. > > Change in [v1] > > * https://lore.kernel.org/lkml/1a5fc7e9-39fe-e527-efc3-1ea990bbb53b@quicinc.com/ > * Posted initial fixup for BAM revision register read handling > drivers/dma/qcom/bam_dma.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/dma/qcom/bam_dma.c b/drivers/dma/qcom/bam_dma.c > index c14557efd577..d227b4f5b6b9 100644 > --- a/drivers/dma/qcom/bam_dma.c > +++ b/drivers/dma/qcom/bam_dma.c > @@ -1199,11 +1199,11 @@ static int bam_init(struct bam_device *bdev) > u32 val; > > /* read revision and configuration information */ > - val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION)); > - if (!bdev->num_ees) > + if (!bdev->num_ees) { > + val = readl_relaxed(bam_addr(bdev, 0, BAM_REVISION)); > bdev->num_ees = (val >> NUM_EES_SHIFT) & NUM_EES_MASK; > - > - bdev->bam_revision = val & REVISION_MASK; > + bdev->bam_revision = val & REVISION_MASK; > + } > > /* check that configured EE is within range */ > if (bdev->ee >= bdev->num_ees) > -- > 2.34.1 >