Expanding my kindle storage with mmc_spi

[saucesaft]

First, an introduction, i have been lurking around these forums for a while but i didn't had an account, so hello

This post is just a part of a personal project im trying to do in converting my kindle into a kind of "cyberdeck". My primary goal is to have plenty of storage in it so i began searching for ways to do it.

I saw posts of people replacing the internal eMMC chip in their kindle, and although it is a great idea, i'm no soldering BGA expert to accomplish that (also, my kindle is a KT4, so i think there's no documented attempt in this model).

Another approach could be finding the solder points of a usb port inside of the kindle (which from what i've seen, happens to be more common on models with a 3G modem variant) which i think the KT4 doesn't have (correct me if they do).

So i began investigating the CPU on my kindle and found out it is an imx6 SoloLite, which has SPI capabilities (the same communication protocol used by SD Cards). I ssh'd into my kindle and found out that there are indeed spi ports "exposed" but the kernel was compiled with only kernel-space use of SPI, in contrast with i2c. So no spidev approach, unless i recompile the kernel with userspace SPI. I could do this and was about to, until i found "mmc_spi.c", a file in the linux kernel source describing a device tree overlay (kind of like a plugin) that itself supports mounting SD cards connected through SPI ports directly into the filesystem, neat right?

More specifically i found this tutorial for the raspberry pi demonstrating how it could be used. Although i was not going to follow this tutorial step-by-step, it served as a guide that i could adapt to the kindle.

I needed a device-tree-compiler, which i already got working by manually installing the respective armel debian package, my next step would be identifying the actual SPI test points in the back of the board.

So here's my question, how would i go in identifying this specific ports?

Thanks! and sorry for the long preamble to the question, wanted to give context.

[katadelos]

A Kindle is a really crappy candidate for this, especially a KT4.

You’re correct in mentioning that the SoC would support the capabilities that you’re after but it’s not a given that the relevant pins are broken on as a test point on the PCB in the first place or that they’re not already used by one of the built in peripherals.

I’m not sure that it’s even possible to edit/reflash the DTB on the later devices (PW4, KT4 onwards) without hard bricking the device due to the whole secure boot thing?

For this use case I’d seriously consider using a Kobo instead - contrast having to figure out a novel, low level method of adding storage vs just popping out the SD card and cloning it to a larger one.

[Quoth]

Newer ereaders may have 8 G or 32 G Flash. Some Kobos do use internal SD cards. The Original H2O has SD card slot.

I'm experienced at SM soldering & editing FW and I'd not try to customise a Kindle like this.

[saucesaft]

Originally Posted by katadelos

A Kindle is a really crappy candidate for this, especially a KT4.

You’re correct in mentioning that the SoC would support the capabilities that you’re after but it’s not a given that the relevant pins are broken on as a test point on the PCB in the first place or that they’re not already used by one of the built in peripherals.

I’m not sure that it’s even possible to edit/reflash the DTB on the later devices (PW4, KT4 onwards) without hard bricking the device due to the whole secure boot thing?

For this use case I’d seriously consider using a Kobo instead - contrast having to figure out a novel, low level method of adding storage vs just popping out the SD card and cloning it to a larger one.

Yeah, i know the KT4 is not the perfect model for this, even a kindle, but it is what i have in hand right now and at least want to give it a try. Before accidentally bricking my kindle, can you tell me more about the secure boot implementation in the kindle? Is there a thread were i can read more about this? Because if i can easily flash DTBs on my kindle, my next step would be to hack-off a rudimentary oscilloscope with an arudino and start searching for the SPI ports. My idea is to use the file "arch/arm/boot/dts/imx6sl.dtsi" (which has the definitions of the 4 SPI ports in software) inside of the source of the linux kernel to create "recognizable" SPI signals as a driver for the kernel, so that i can search them and identify the ports (if do they exist) with my oscilloscope.