linux-kernel - NXP imx6ull nonalignment buffer question

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Message-ID: <CAOf5uwns3YZMY5xhM+o0rNvtTqEDwCbua5HuSy-LBwgZq_eWYg@mail.gmail.com>
Date:   Mon, 9 Jan 2023 14:02:14 +0100
From:   Michael Nazzareno Trimarchi <michael@...rulasolutions.com>
To:     Bough Chen <haibo.chen@....com>, Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-mmc@...r.kernel.org, Ulf Hansson <ulf.hansson@...aro.org>
Subject: NXP imx6ull nonalignment buffer question

Hi Haibo

Working on imx6ulz design and found that if I send a sdio packet using
the sdio_writesb the adma driver tries to handle it with two dma
descriptors. The first one filled with the bytes up to 3 to cover the
misalign and then another buffer descriptor

  offset = (SDHCI_ADMA2_ALIGN - (addr & SDHCI_ADMA2_MASK)) &
                         SDHCI_ADMA2_MASK;
                if (offset) {
                        if (data->flags & MMC_DATA_WRITE) {
                                buffer = sdhci_kmap_atomic(sg);
                                memcpy(align, buffer, offset);
                                sdhci_kunmap_atomic(buffer);
                        }

                        /* tran, valid */
                        __sdhci_adma_write_desc(host, &desc, align_addr,
                                                offset, ADMA2_TRAN_VALID);

                        BUG_ON(offset > 65536);

                        align += SDHCI_ADMA2_ALIGN;
                        align_addr += SDHCI_ADMA2_ALIGN;

                        addr += offset;
                        len -= offset;
                }

In 48.7.4 Data Length Setting
For either ADMA (ADMA1 or ADMA2) transfer, the data in the data buffer must be
word aligned, so the data length set in the descriptor must be a
multiple of 4. I have noticed that this code does not work as
expected.

Did you have any feedback?

Michael