On Thu, 16 Sept 2021 at 11:47, Wenbin Mei [off-list ref] wrote:

On Tue, 2021-09-14 at 10:46 +0200, Ulf Hansson wrote:

quoted

On Wed, 8 Sept 2021 at 03:32, Wenbin Mei [off-list ref]
wrote:

quoted

Due to the influence of the corner IC and vcore voltage, for the
stability
of HS400 mode, we Add HS400 mode online tuning support for mediatek
mmc
host.

My apologies, but I am not familiar with what 'HS400 online tuning'
is? Can you please elaborate on this?

Is it specific for a Mediatek eMMC controller - or is a common eMMC
feature that is described in the eMMC spec?

According to JEDEC Spec, there is no need to do tuning under HS400 mode
since the Rx signal is aligned with the DS signal. However, MediaTek's
IC need set its "DS delay" internally to ensure it can latch Rx signal
correctly.
In previous version, We provide an "hs400-ds-delay" in device tree to
cover different chipset/PCB design, and it works fine in most cases.
But, with the development of process technology and the big VCore
voltage scale range(may have 0.7V/0.6V/0.55V), it is difficult to find
a suitable "hs400-ds-delay" to cover all of IC corner
cases(SSSS/TTTT/FFFF).
So that We must have the ability to do hs400 online tuning.
It is specific for the Mediatek eMMC controller which support HS400
mode.

I see, thanks for clarifying. Please put some of this information in
the commit message for the next version, it certainly helps to
understand.

[...]

quoted

quoted

+static int msdc_send_cxd_data(struct mmc_card *card, struct
mmc_host *host)
+{
+       struct mmc_request mrq = {};
+       struct mmc_command cmd = {};
+       struct mmc_data data = {};
+       unsigned int len = 512;
+       struct scatterlist sg;
+       u8 *ext_csd;
+
+       ext_csd = kzalloc(len, GFP_KERNEL);
+       if (!ext_csd)
+               return -ENOMEM;
+
+       mrq.cmd = &cmd;
+       mrq.data = &data;
+
+       cmd.opcode = MMC_SEND_EXT_CSD;
+       cmd.arg = 0;
+       cmd.flags = MMC_RSP_SPI_R1 | MMC_RSP_R1 | MMC_CMD_ADTC;
+
+       data.blksz = len;
+       data.blocks = 1;
+       data.flags = MMC_DATA_READ;
+       data.sg = &sg;
+       data.sg_len = 1;
+
+       sg_init_one(&sg, ext_csd, len);
+       mmc_set_data_timeout(&data, card);
+       mmc_wait_for_req(host, &mrq);
+
+       kfree(ext_csd);
+
+       if (cmd.error)
+               return cmd.error;
+       if (data.error)
+               return data.error;
+
+       return 0;

Why do we need to send a MMC_SEND_EXT_CSD command, exactly?

Why can't mmc_send_tuning() work here too? What does the eMMC spec
state about this?

The CMD21 is illegal under hs400 mode so that cannot use the
mmc_send_tuning(). The CMD8 is suitable because it will receive 1 block
of non-zero data.

I see.

In that case it seems better to use mmc_get_ext_csd(), from the core,
rather than open coding the above. To do that, you also need to move
the declaration of mmc_get_ext_csd() to include/linux/mmc/host.h.

[...]

Kind regards
Uffe